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POSTGRADUATE PATHOLOGY - EXAM ANSWERS (APED FORMAT)

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Q1 & Q6. BIOMEDICAL WASTE MANAGEMENT (and Recent Amendments)

Definition

Legal Framework

• Governed by Biomedical Waste Management Rules, 2016 (amended 2018, 2019) under the Environment Protection Act, 1986
• Replaced older BMW Rules 1998

Classification of Biomedical Waste (BMW Rules 2016 - 4 Categories)

Treatment Methods

1. Incineration - Yellow category; destroys pathogens and reduces volume; produces fly ash
2. Autoclaving - Steam sterilization at 134°C, 30 min; for Red and Blue categories
3. Microwaving - Electromagnetic waves generate heat; for general BMW
4. Chemical disinfection - Liquid BMW; 1% hypochlorite for blood/body fluids
5. Deep burial - Remote areas only; for Yellow category
6. Plasma pyrolysis - High-tech disposal, produces syngas

Recent Amendments (2018, 2019)

• Addition of a 5th category (Black) for general solid non-hazardous waste from healthcare
• Mandatory bar-coding of bags/containers for traceability
• Online reporting to Pollution Control Boards via web portal
• Phase-out of chlorinated plastics for waste bags
• All healthcare facilities to be connected to Common Biomedical Waste Treatment Facilities (CBWTFs)
• Liquid BMW from labs, blood banks: treat with chemical disinfection before drain disposal
• Inclusion of COVID-19 waste protocols (2020 amendment): double-layered yellow bags, separate collection

Key Responsibilities

• Occupier (hospital) = generator; must segregate at source
• Operator of CBWTF = transporter/processor
• SPCBs/PCCs = regulatory authority

Important Points for Exam

• "Cradle to grave" principle
• Annual report to SPCB by January 31
• Accident reporting within 24 hours
• BMW should NOT be mixed with municipal solid waste

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Q2. ADVANCES IN MINIMALLY INVASIVE AUTOPSY AND ITS LIMITATIONS

Definition

Rationale

• Increasing refusal of conventional autopsy (religious, cultural, cosmetic concerns)
• Declining autopsy rates worldwide (<10% in many centers)
• Need for cause-of-death data in resource-limited settings (especially child mortality)

Types / Techniques

• 3D reconstruction of internal organs
• Excellent for: trauma, fractures, pneumothorax, gas embolism, bleeding, foreign bodies
• System: "Virtopsy" (Virtual autopsy) - CT + MRI + surface scanning
• Limitation: Cannot differentiate agonal from antemortem changes; poor soft tissue contrast

• Better soft tissue delineation than CT
• Good for CNS, cardiac lesions, white matter diseases
• Used in fetal/perinatal MIA (replaces infant autopsy well)
• Limitation: Costly, not widely available, iron artifacts after embalming

• Core needle biopsy, fine needle aspiration, bone marrow biopsy
• Done under imaging (US/CT) guidance
• Used by WHO/Global Child Health programs for verbal autopsy
• Sites: lung, liver, brain, spleen, heart, lymph node, bone marrow

• Vitreous humor biochemistry (best preserved: glucose, Na, K, urea)
• Vitreous glucose - diabetes; vitreous Na/K ratio - dehydration
• Postmortem toxicology: blood, urine, vitreous for drugs/poisons

• Genetic testing (next-generation sequencing) from cardiac tissue/blood
• Channelopathies (LQTS, Brugada) - cause sudden unexplained death
• Postmortem molecular autopsy in sudden cardiac death: 25-35% yield

• Needle aspiration of lung, blood, CSF
• Used in child mortality surveillance in Africa (CHAMPS project)

Limitations of MIA

1. Cannot assess all organ systems comprehensively
2. Sampling error - patchy lesions may be missed
3. PMCT poor at detecting: pulmonary edema, myocardial infarction (early), pneumonia
4. MRI: time-consuming, expensive
5. Post-mortem changes complicate histological interpretation
6. Legal/medicolegal purposes - conventional autopsy still required
7. Cannot replace the "clinico-pathological correlation" of full autopsy
8. Operator skill-dependent (biopsy guidance)
9. Tissue decomposition limits molecular analysis
10. No gold standard protocols exist yet

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Q3. MICROWAVE TECHNOLOGY IN PATHOLOGY

Principle

Advantages Over Conventional Methods

• Speed (minutes vs hours/days)
• Better morphological preservation
• Enhanced penetration of reagents

Applications in Pathology

• Formalin fixation: conventionally 12-24 hours → microwave: 5-30 minutes
• Rapid intraoperative diagnosis
• Cross-linking proteins rapidly
• Useful in frozen section when cryostat is unavailable

• Entire processing cycle (dehydration, clearing, infiltration) in 1-3 hours vs overnight
• Commercial microwave tissue processors available

• Most important application
• Formalin masking of antigenic epitopes is reversed by microwave heating in citrate buffer (pH 6.0) or EDTA (pH 9.0)
• Essential for IHC staining quality
• Protocols: 600-750W, 10-20 min in citrate buffer

• H&E, special stains (PAS, ZN, Masson's Trichrome) - staining time reduced from hours to minutes
• Better dye penetration
• Used in: Reticulin stain, silver stains

• Bone specimens: EDTA decalcification 7-14 days → microwave: 1-3 days
• Better antigen preservation compared to acid decalcification

• Renal biopsies: frozen sections + microwave fixation instead of IF on fresh tissue

• Enhances probe penetration
• Reduces hybridization time

• Rapid glutaraldehyde fixation for EM specimens

• Microwave treatment of BMW (Red/Blue category) before shredding

Disadvantages / Limitations

• Uneven heating (hot spots) - overcome by rotating platform and water bath
• Temperature monitoring essential (60-65°C optimal; >70°C damages morphology)
• Not suitable for very large specimens
• Equipment calibration required
• Cannot replace conventional processing for large tissue volumes

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Q4. FLUORESCENT IN-SITU HYBRIDIZATION (FISH) AND CHROMOGENIC IN-SITU HYBRIDIZATION (CISH)

FLUORESCENT IN-SITU HYBRIDIZATION (FISH)

• DNA or RNA probe labeled with fluorescent dye (fluorochrome) hybridizes to complementary sequence on target chromosome/cell in a tissue section or metaphase spread
• Visualized under fluorescence microscope (UV light)

1. Prepare specimen (tissue section, cytology smear, blood film)
2. Pretreatment (protease digestion, heat denaturation at 75-85°C)
3. Apply labeled probe + hybridization (overnight at 37°C)
4. Post-hybridization washes (remove non-specific binding)
5. Counterstain with DAPI (stains DNA blue)
6. Visualize with fluorescence microscope

1. HER2 amplification in breast and gastric cancer (gold standard with IHC equivocal 2+)
2. BCR-ABL translocation - t(9;22) in CML (Philadelphia chromosome)
3. ALK rearrangement in lung adenocarcinoma and ALCL
4. MYCN amplification in neuroblastoma (prognostic)
5. SYT-SSX in synovial sarcoma
6. EWS-FLI1 in Ewing's sarcoma
7. COL1A1-PDGFB in dermatofibrosarcoma protuberans
8. Prenatal diagnosis - rapid aneuploidy detection (trisomy 13, 18, 21; monosomy X)
9. 1p/19q deletion in oligodendroglioma
10. EGFR amplification in glioblastoma

• High sensitivity and specificity
• Can detect gene amplification, deletion, translocation, polysomy
• Works on FFPE tissue
• Rapid (24-48 hours)

• Expensive equipment (fluorescence microscope with filters)
• Signal fades over time (non-permanent)
• Cannot visualize morphology simultaneously
• Requires expertise
• Not suitable for routine labs in developing countries

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NOTE ON CHROMOGENIC IN-SITU HYBRIDIZATION (CISH)

• Same as FISH but probe is labeled with enzyme (HRP or AP) instead of fluorochrome
• Chromogenic substrate (DAB = brown; Fast Red = red) produces permanent color signal
• Viewed under ordinary light microscope

1. Tissue preparation + denaturation
2. Hybridization with enzyme-labeled probe
3. Chromogenic detection (DAB or NBT/BCIP)
4. Counterstain with hematoxylin
5. View under brightfield microscope

• Probe labeled with dinitrophenol → anti-DNP antibody → silver deposition
• Black signal on light microscope
• Used for HER2 by Ventana automated platforms

• HER2 amplification (validated equivalent to FISH)
• MYCN in neuroblastoma
• Automated platforms (Ventana SISH)
• Dual-color CISH (D-CISH): red for HER2 gene, blue for chromosome 17 centromere

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Q5. LABORATORY SAFETY PRACTICES

Classification of Laboratory Hazards

1. Biological (infectious agents)
2. Chemical (corrosives, flammables, carcinogens)
3. Physical (fire, radiation, electrical, mechanical)
4. Ergonomic hazards

Biosafety Levels (BSL 1-4)

Universal Precautions

• ALL specimens treated as potentially infectious
• Hand hygiene: before and after every procedure
• PPE: gloves, lab coat, eye protection, mask
• No eating/drinking/smoking in lab
• No mouth pipetting

Chemical Safety (OSHA/GHS Standards)

• Safety Data Sheets (SDS) for every chemical
• Fume hoods for volatile chemicals (xylene, formalin, acetone)
• Formalin exposure limit: 0.75 ppm TWA (OSHA); known carcinogen (Group 1, IARC)
• Xylene: flammable, hepatotoxic - use xylene substitutes
• Proper labeling, storage (flammables in flameproof cabinets)
• Acid/alkali in separate cabinets; neutralize before disposal

Biological Safety Cabinets (BSC)

• Class I: inward airflow, protects worker, not product
• Class II: HEPA filtered; most common in pathology labs (Type A, B)
• Class III: totally enclosed glove boxes (BSL-4)

Sharps Safety

• Never re-cap needles with two hands
• Puncture-proof sharps containers (fill to 3/4 only)
• Safety-engineered needles and lancets
• Needle-stick protocol: squeeze blood, wash with soap, report, PEP within 2 hours

Radiation Safety (for labs using radioisotopes)

• ALARA principle (As Low As Reasonably Achievable)
• Time, Distance, Shielding (inverse square law)
• TLD badges (Thermoluminescent dosimeter)
• Maximum permissible dose: 20 mSv/year occupational

Fire Safety

• RACE: Rescue, Alarm, Confine, Evacuate
• PASS: Pull, Aim, Squeeze, Sweep (fire extinguisher)
• Classes: A (ordinary), B (flammable liquids), C (electrical), D (metals)

Electrical Safety

• Ground all equipment
• No water near electrical equipment
• Circuit breakers, GFCI outlets
• Regular equipment maintenance

Ergonomic Safety

• Adjustable workstations; anti-fatigue mats
• Regular breaks; proper pipette technique
• Microscope posture guidelines

Emergency Procedures

• Eyewash stations within 10 seconds travel time
• Safety showers for chemical spill on body
• Spill kits for biological (bleach-based) and chemical spills
• Lab incident reporting system

Quality and Safety Management

• Standard Operating Procedures (SOPs) for all procedures
• Regular safety audits
• Training and competency assessment
• Incident/near-miss reporting culture

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Q7 & Q35. LABORATORY INVESTIGATIONS IN COMA

Definition

AEIOU-TIPS Mnemonic (Causes)

Immediate (Emergency) Investigations

• Fingerstick glucose (immediate - rule out hypoglycemia, most common reversible cause)
• Pulse oximetry + ABG (SpO2, PaO2, PaCO2, pH, BE)
• ECG

• CT brain (non-contrast emergency): stroke, hemorrhage, herniation, hydrocephalus, mass
• MRI brain + DWI: superior for posterior fossa, encephalitis, RPLS

1. Immediate: glucose stick, O2 sat, ECG, IV access
2. Urgent (within 30 min): blood sugar, electrolytes, ABG, CBC, RFT, LFT, toxicology, blood culture
3. Emergent (1-2 hrs): CT brain, CSF (if indicated), specific hormone tests
4. EEG: non-convulsive status epilepticus

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Q8, Q9, Q10, Q29, Q36, Q38, Q40. AUTOMATION IN CLINICAL PATHOLOGY

Introduction

Types of Automation

• Impedance (Coulter principle): RBC, WBC, platelets counted by change in electrical resistance
• Light scattering (LASER): cell size (FSC), complexity (SSC), fluorescence (stained cells)
• Peroxidase cytochemistry: neutrophils/monocytes
• Examples: Sysmex XN series, Abbott CELL-DYN, Beckman Coulter DxH

• CBC: WBC, RBC, Hb, Hct, MCV, MCH, MCHC, RDW, PLT, MPV
• 5-part WBC differential: neutrophils, lymphocytes, monocytes, eosinophils, basophils
• Reticulocyte count (automated with RNA-staining dyes)
• Immature granulocyte count, NRBC, nucleated RBC

• Colorimetric, turbidimetric, enzymatic, immunoassay methods
• STAT + routine samples simultaneously
• Examples: Beckman Coulter AU series, Roche Cobas, Abbott Architect
• Parameters: glucose, urea, creatinine, uric acid, liver enzymes, proteins, lipids, electrolytes

• ISE (Ion Selective Electrode): Na, K, Cl, Ca, Li - direct potentiometry
• Enzymatic photometry: biochemistry analytes
• ELISA on analyzer: hormones, cardiac markers
• Turbidimetry: proteins (CRP, immunoglobulins)

• ECLIA (Electrochemiluminescence): Roche Elecsys - hormones, cardiac markers, infectious disease, tumor markers
• CLIA (Chemiluminescence immunoassay): Abbott Architect i series
• FEIA (Fluorescent enzyme immunoassay): allergy testing
• Analytes: TSH, T3/T4, LH, FSH, cortisol, HCG, Troponin I/T, PSA, AFP, CA-125, HIV Ag/Ab

• Optical clot detection or mechanical impedance
• Parameters: PT, aPTT, INR, fibrinogen, D-dimer, factor assays
• Examples: Stago STA-R series, Instrumentation Laboratory ACL

• Automated urine chemistry analyzers (reflectance photometry on dipstick)
• Automated microscopy: Iris iQ200, Sysmex UF analyzers
• Particle recognition by image analysis + flow cytometry

• MALDI-TOF MS: species identification in 10-15 minutes from culture colony
• Blood culture systems: BacT/ALERT, BACTEC (continuous monitoring)
• Automated sensitivity testing: VITEK 2, Phoenix - MIC determination
• Molecular diagnostics: Automated extraction + PCR (GeneXpert, FilmArray)

• Pre-analytical: sample registration, centrifugation, aliquoting, decapping
• Analytical: transport to analyzers on conveyor tracks
• Post-analytical: re-capping, storage, disposal
• Examples: Beckman Coulter Power Express, Roche cobas connection module

Advantages of Automation

1. Increased throughput (hundreds of samples/hour)
2. Reduced human error - precision and accuracy
3. Reproducibility (CV < 2%)
4. Shorter TAT (Turnaround Time)
5. Reduced sample volume needed
6. Flagging of abnormal results
7. Digital record-keeping, LIS integration
8. Reduces exposure to biohazardous material

Disadvantages / Limitations

1. High initial capital cost
2. Maintenance and calibration requirements
3. Reagent lock-in to manufacturer
4. Cannot fully replace expert morphological review
5. Errors in flagging atypical cells (need manual review)
6. Power dependency
7. Technical expertise for troubleshooting
8. Interferences (hemolysis, lipemia, icterus - HLI indices important)

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Q11. AMNIOCENTESIS AND CHORIONIC VILLUS BIOPSY (CVS)

AMNIOCENTESIS

• Ultrasound guidance (real-time)
• 20-22 gauge spinal needle, transabdominal approach
• 15-20 mL amniotic fluid withdrawn
• Fluid: fetal cells (amniocytes) + cell-free amniotic fluid

• Fetal cells: cultured for karyotyping (2-3 weeks), FISH (48-72 hours), array CGH
• Amniotic fluid biochemistry: AFP (neural tube defects), AChE (open NTD)
• Cell-free DNA analysis
• Enzyme assays for metabolic disorders

1. Advanced maternal age (≥35 years) - risk of trisomies
2. Previous child with chromosomal abnormality
3. Parental chromosomal rearrangement
4. Abnormal maternal serum screening (triple/quadruple test, NIPT)
5. Abnormal ultrasound findings
6. Risk of sex-linked disorders
7. Risk of single gene disorders (inborn errors, CF, sickle cell)
8. Neural tube defect family history

• Chromosomal: trisomy 21, 18, 13; Turner, Klinefelter; translocations
• Single gene: CF, sickle cell, PKU, inborn errors
• Biochemical: AFP elevated → NTD; low → Down syndrome
• Normal karyotype does NOT exclude all abnormalities (only detects chromosomal)

1. Fetal loss: 0.5-1% (1 in 100-200)
2. Amniotic fluid leak
3. Chorioamnionitis (infection)
4. Maternal injury
5. Rh sensitization (give anti-D to Rh-negative mothers)
6. Fetal injury (rare with US guidance)
7. Failure of cell culture
8. Culture contamination
9. Maternal cell contamination: misinterpretation

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CHORIONIC VILLUS SAMPLING (CVS)

• Transcervical CVS: catheter through cervix under US guidance (before 13 weeks)
• Transabdominal CVS: needle through abdomen (after 13 weeks or if cervix inaccessible)
• 10-25 mg tissue obtained

• Direct preparation: immediate karyotype in 24-48 hours (less accurate, limited metaphases)
• Long-term culture: accurate karyotype in 7-10 days
• Molecular: FISH, array CGH, PCR for gene mutations
• Enzyme assays: direct from villi

• Earlier diagnosis (10-13 vs 15-20 weeks)
• Faster results
• More material available for multiple tests
• Earlier termination if abnormal (less morbid)

1. Higher fetal loss rate: 1-2% (higher than amniocentesis)
2. Confined placental mosaicism (CPM): 1-2%; placental chromosome abnormality not present in fetus; may require follow-up amniocentesis
3. Limb defects: associated with procedures before 9 weeks (no longer done before 10 weeks)
4. Infection (chorioamnionitis)
5. Rh sensitization
6. Maternal cell contamination
7. Cannot detect open NTD (no AFP in CVS; need follow-up US)
8. Cannot assess AFP levels

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Q12 & Q16. IHC IN MALIGNANT SPINDLE CELL TUMORS / SOFT TISSUE SARCOMAS

Introduction

Classification of Spindle Cell Soft Tissue Tumors

Key IHC Markers and Their Significance

Diagnostic Algorithm for Spindle Cell STS

SPINDLE CELL TUMOR
├── Vimentin + → Mesenchymal origin confirmed
│
├── DOG1/CD117 + → GIST
├── Desmin+, Myogenin+ → RMS
├── h-Caldesmon+, SMA+ → Leiomyosarcoma
├── S-100+, SOX10+ → MPNST / Melanoma
├── TLE1+, EMA/CK focal + → Synovial Sarcoma
├── MDM2+, CDK4+ → Dediff Liposarcoma
├── STAT6 nuclear + → SFT
├── MUC4+ → LGFMS
├── INI1 loss → Epithelioid Sarcoma
├── CD31/34/ERG+ → Angiosarcoma
└── CD99+, NKX2.2+ → Ewing's sarcoma

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Q14. HPLC (HIGH PERFORMANCE LIQUID CHROMATOGRAPHY) APPLICATIONS

Principle

Types

• Reverse-phase HPLC: most common; non-polar stationary phase (C18), polar mobile phase
• Ion-exchange HPLC: separates by charge (used for Hb variants)
• Size-exclusion (gel filtration): separates by molecular size
• Affinity HPLC: uses specific ligand-receptor interaction

Applications in Pathology/Medicine

• HbA1c measurement: gold standard for glycated hemoglobin; NGSP/IFCC certified
• Hemoglobin variant analysis: HbS (sickle cell), HbC, HbD, HbE, HbF
• Diagnosis of thalassemia (HbA2 quantification; >3.5% in beta-thal trait)
• Neonatal screening programs
• Detection of rare Hb variants
• Bio-Rad Variant II = standard instrument

• Cyclosporine, tacrolimus (immunosuppressants)
• Phenytoin, phenobarbitone, carbamazepine (anti-epileptics)
• Aminoglycosides
• Methotrexate

• Fat-soluble: Vitamin A, D, E, K quantification
• Water-soluble: B vitamins (B1, B2, B6, B12, Folate)

• Drug abuse screening and confirmation
• Heavy metal analysis
• Pesticide detection

• Inborn errors of metabolism (phenylketonuria, MSUD)
• Aminoacidopathies

• Urine organic acids in metabolic disorders

• Cholesterol, fatty acids
• Corticosteroids, sex hormones (plasma)
• Bile acids (serum and urine)

• Catecholamines (pheochromocytoma diagnosis)
• Vanillylmandelic acid (VMA), homovanillic acid (HVA) - neuroblastoma
• 5-HIAA (carcinoid syndrome)
• Metanephrines

• Post-mortem drug/poison analysis

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Q15. SERUM PROTEIN ELECTROPHORESIS (SPEP)

Principle

Normal Bands (Anode to Cathode)

Abnormal Patterns and Clinical Significance

• Single sharp tall peak in gamma (or beta) region
• Homogeneous immunoglobulin from single clone
• Causes: Multiple myeloma, Waldenstrom's macroglobulinemia, MGUS, amyloidosis, lymphoma
• Follow-up: Immunofixation electrophoresis (IFE) to type the M protein
• Quantify M-protein for monitoring disease and treatment response

• Broad-based increase in gamma region
• Causes: Chronic infections (TB, HIV, SBE), liver disease (cirrhosis), autoimmune diseases (SLE, RA)

• Decreased albumin band
• Causes: Malnutrition, nephrotic syndrome, cirrhosis, malabsorption, chronic inflammation

• Decreased albumin (loss in urine)
• Increased alpha-2 (macroglobulin - too large to pass glomerular filter)
• Decreased gamma globulins
• "Low albumin, high alpha-2" pattern

• Decreased albumin
• Increased alpha-1 and alpha-2 bands
• Increased fibrinogen (if plasma used)

• Decreased albumin
• Beta-gamma bridging ("beta-gamma fusion") - IgA migrates to beta region and merges with gamma
• May have polyclonal gammopathy

• Absent/decreased alpha-1 band
• Confirm with AAT phenotyping (PiZZ genotype)
• Associated with emphysema (young adults), liver cirrhosis

• Decreased alpha-2 band (haptoglobin consumed by Hb-Hp complexes)

• Increased transferrin → increased beta band

Clinical Uses

• Screening for monoclonal gammopathy
• Chronic disease monitoring
• Nutritional assessment
• Liver function evaluation
• Autoimmune disease workup

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Q17. RT-PCR IN CLINICAL DIAGNOSIS

Definition

Principle - Two Steps

1. Reverse Transcription: RNA → cDNA by enzyme reverse transcriptase (RT) using oligo-dT or random hexamer primers
2. PCR Amplification: cDNA amplified by Taq polymerase with specific primers

Types

• Conventional RT-PCR: end-point detection on gel electrophoresis
• Real-time RT-PCR (qRT-PCR): quantitative; measures fluorescence during each cycle; gold standard

Applications in Clinical Diagnosis

• COVID-19 (SARS-CoV-2): WHO gold standard; detects ORF1ab, N gene, E gene; sensitivity ~70-90%
• HIV viral load: quantifies HIV RNA; monitors treatment response (target <50 copies/mL)
• HCV RNA: diagnosis of active infection; quantification; genotyping; treatment monitoring
• HBV viral load: monitoring
• Influenza A/B: subtyping (H1N1, H3N2, H5N1)
• Dengue, Zika, Chikungunya: detection in acute phase
• RSV, rhinovirus, metapneumovirus: respiratory panel
• Ebola, MERS-CoV: high-risk pathogens
• TB (GeneXpert MTB/RIF): rapid detection + rifampicin resistance
• HPV genotyping (see Q18)

• BCR-ABL (Philadelphia chromosome) in CML: monitoring MRD (minimal residual disease); target <0.01% (molecular remission)
• PML-RARA in APL: diagnosis and MRD monitoring
• EGFR mutations in lung cancer: exons 18-21; guides gefitinib/erlotinib
• BRAF V600E in melanoma, colorectal, thyroid: targeted therapy
• KRAS, NRAS mutations: colorectal cancer (anti-EGFR resistance)
• NPM1, FLT3-ITD in AML: prognostic and MRD

• Fragile X syndrome (FMR1 CGG repeat expansion)
• Myotonic dystrophy, Huntington's disease (triplet repeats)
• Duchenne muscular dystrophy (DMD gene deletions)

• Measure mRNA levels
• Differentiate tumor subtypes by expression profiling

• Extremely sensitive (detects single copy)
• Quantitative (viral load, MRD)
• Rapid (3-4 hours)
• Can be multiplexed
• Works on poor-quality or degraded RNA

• RNA is unstable; careful specimen handling required
• Risk of contamination (false positives)
• Requires skilled personnel
• Inhibitors in clinical samples can cause false negatives
• Does not detect non-expressed mutations

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Q18. MOLECULAR TESTING FOR HPV IN CERVICAL SCREENING

Background

• HPV (Human Papillomavirus) - causally linked to 99.7% of cervical cancers
• High-risk HPV (hrHPV): types 16, 18 (70% of cervical cancers), 31, 33, 45, 52, 58
• Low-risk HPV: types 6, 11 (condyloma acuminata)
• Cervical cancer is 4th most common cancer in women worldwide

Why Molecular HPV Testing?

Methods of HPV Molecular Testing

• Signal amplification method (not true PCR)
• Probe hybridizes to HPV DNA → RNA:DNA hybrid captured → luminescence measured
• FDA-approved; detects 13 hrHPV types collectively (not individual genotyping)
• Gold standard for decades; sensitivity ~90%

• Real-time PCR
• Simultaneously identifies HPV 16, HPV 18 separately + pool of 12 other hrHPV types
• FDA-approved for primary screening + reflex testing
• First test approved for primary HPV screening alone (without Pap)

• Detects E6/E7 mRNA (not DNA) - reflects active transcription
• TMA (Transcription-Mediated Amplification)
• Higher specificity; reduces false positives from transient infections
• E6/E7 oncoproteins drive carcinogenesis

• Automated real-time PCR
• Cartridge-based, near-patient testing
• Identifies HPV 16, 18/45, + 12 other hrHPV

• Genotype-specific
• Identifies all 28 or 37 HPV genotypes individually
• Used in research and epidemiology

Current Screening Guidelines (WHO 2021 / ACS 2020)

Management of HPV-Positive Results

• HPV-16 or HPV-18 positive → Colposcopy directly (high cancer risk)
• Other hrHPV positive + cytology negative → Repeat co-testing in 1 year
• Other hrHPV positive + ASC-US or worse → Colposcopy

Role in Low-Resource Settings

• Self-sampling + HPV PCR: effective for hard-to-reach populations
• WHO "90-70-90 strategy" for cervical cancer elimination by 2030:
  • 90% girls vaccinated by age 15
  • 70% women screened with high-performance test by age 35 (and again at 45)
  • 90% women with cervical disease treated

Molecular Testing Significance

• Detects transforming infection before cytological abnormality
• High NPV (99.7%) - long interval before re-testing
• Identifies women at risk for CIN3+ and invasive cancer
• Guides triage for colposcopy

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Q19. HEPATORENAL SYNDROME (HRS)

Definition

• Acute kidney injury (AKI) without structural kidney disease
• Intense renal vasoconstriction
• Marked systemic and splanchnic vasodilation
• Reversible in principle (kidneys are normal) - if liver transplanted, kidneys recover

Pathophysiology

Cirrhosis
→ Portal hypertension
→ Splanchnic vasodilation (NO, prostacyclin)
→ Decreased effective arterial blood volume (EABV)
→ Baroreceptor activation → RAAS + SNS + ADH
→ Renal vasoconstriction (angiotensin II, endothelin, adenosine)
→ GFR falls
→ HRS

Classification (ICA 2015 Criteria)

• Rapid deterioration: serum creatinine doubles to >2.5 mg/dL in <2 weeks
• Precipitants: SBP, GI bleeding, hepatitis
• Median survival: 2-4 weeks without treatment
• More severe

• Slowly progressive
• Creatinine 1.5-2.5 mg/dL
• Associated with refractory ascites
• Median survival: 4-6 months

Diagnostic Criteria (ICA 2015)

1. Cirrhosis with ascites OR acute liver failure
2. Diagnosis of AKI (creatinine increase ≥0.3 mg/dL in 48 hours OR ≥50% increase from baseline in 7 days)
3. No improvement after 2 days of albumin infusion + diuretic withdrawal
4. No shock
5. No nephrotoxic drugs
6. No macroscopic signs of structural kidney disease (proteinuria <500 mg/day, no hematuria, normal USG)

Laboratory Findings

• Serum creatinine: elevated, rising
• Serum Na: hyponatremia (dilutional)
• Urine Na: <10 mEq/L (intense tubular Na reabsorption)
• Urine osmolality > plasma osmolality
• Urine: no proteinuria, no casts (normal sediment)
• FENa: <1% (pre-renal pattern)
• Liver function: very poor (low albumin, high bilirubin, prolonged PT)
• Serum K: may be elevated (reduced GFR + hypoaldosteronism in some)

Treatment

1. Terlipressin + Albumin (IV): vasopressin analogue + volume expander; 40-50% response; reverses HRS in Type 1
2. Norepinephrine + Albumin: in ICU setting; equivalent to terlipressin
3. Midodrine (oral) + Octreotide + Albumin: outpatient, less effective
4. TIPS (Transjugular Intrahepatic Portosystemic Shunt): reduces portal pressure; used in Type 2
5. Hemodialysis/CRRT: bridge to transplant
6. Liver transplantation: definitive treatment; kidney function recovers in most

Prevention

• Albumin IV with large-volume paracentesis (8g/L ascites removed)
• Albumin + antibiotics for SBP (1.5 g/kg Day 1 + 1 g/kg Day 3)
• Norfloxacin prophylaxis in high-risk cirrhosis

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Q20. LEVEY-JENNINGS CHARTS

Definition

Construction

1. Analyze QC material (known concentration) repetitively (≥20 times) over 20+ days
2. Calculate mean (x̄) and standard deviation (SD) of those values
3. Set control limits: x̄ ± 1SD, ±2SD, ±3SD
4. Plot each subsequent QC value on the chart (Y-axis = result; X-axis = time/run number)
5. Draw horizontal lines at mean, ±1SD, ±2SD, ±3SD

Westgard Rules (Applied to LJ Charts)

Interpretation of Patterns

• Results scatter widely around mean
• No trend or shift
• Causes: unstable reagents, pipetting imprecision, temperature fluctuation, electronic noise

• Trend: gradual drift in one direction (reagent degradation, electrode drift)
• Shift: abrupt displacement to new level (new reagent lot, recalibration error, new analyst)

Uses of LJ Charts

1. Daily QC monitoring
2. Detection of method failure before patient results reported
3. Identifying source of error (reagent vs instrument vs operator)
4. Documenting QC performance over time
5. CAP (College of American Pathologists) accreditation requirement

Important Points

• Two levels of QC recommended (normal and abnormal)
• LJ chart is the visual tool; Westgard rules are the decision criteria
• "In control" ≠ "accurate" (systematic bias may go undetected if mean is set incorrectly)
• Monthly/quarterly review of QC statistics for trend analysis
• QC material: lyophilized serum, commercial controls; not the same as calibrators

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Q21. ROLE OF TUMOR MARKERS IN LABORATORY DIAGNOSIS OF CANCER

Definition

Ideal Tumor Marker Characteristics

• Produced only by tumor (high specificity)
• Detectable at early stage (high sensitivity)
• Levels correlate with tumor burden
• Measurable by simple test
• Short half-life (rapid response to treatment)
• No false positives

Classification and Examples

Uses of Tumor Markers

• PSA for prostate cancer (controversially)
• AFP for HCC surveillance in high-risk (cirrhosis, HBV/HCV)
• CA-125 for ovarian cancer (low specificity)

• β-HCG for choriocarcinoma
• Calcitonin for MTC
• AFP + HCG for germ cell tumors

• AFP, β-HCG, LDH in testicular cancer IGCCCG staging
• PSA level correlates with prostate cancer stage

• Fall after surgery/chemo = good response
• Persistent elevation = incomplete removal
• CEA in colorectal cancer
• PSA in prostate cancer
• CA-125 in ovarian cancer

• Rising PSA after prostatectomy = biochemical recurrence
• Rising CEA after CRC surgery = liver metastasis suspected
• Thyroglobulin rise after thyroid ablation = recurrent/metastatic thyroid cancer

• Target for immunotherapy (CEA-targeted CAR-T cells)

Limitations

1. Low sensitivity for early-stage disease
2. Low specificity (elevated in benign conditions)
3. Not tumor-specific (CEA in many cancers)
4. Inter-laboratory variation in assays
5. Hook effect (very high levels give falsely low reading - dilute sample)

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Q22. CHEMILUMINESCENCE AND ITS APPLICATIONS

Definition

Types

• Luminol, acridinium ester, isoluminol - directly emit light upon oxidation
• Acridinium ester: triggered by H₂O₂ + NaOH
• Very fast (<1 second flash), no enzyme needed

• Enzyme (HRP or AP) generates luminescent substrate
• HRP + H₂O₂ + Luminol: enhanced by phenols
• AP + AMPPD (adamantyl phenyl phosphate dioxetane): 1,2-dioxetane emits sustained light (glow reaction - minutes to hours)
• Used in ELISA-based luminescence

• Light generated by electrochemical reaction on electrode
• Ruthenium (Ru) complex + TPA (tripropylamine) oxidized at electrode → excited Ru* emits light at 620 nm
• Used in Roche Elecsys platform
• Advantages: highly reproducible, quantitative, broad dynamic range

• Natural: Firefly (luciferase + luciferin + ATP + O₂ → oxyluciferin + CO₂ + light)
• Used as reporter gene in molecular biology

Applications in Clinical Laboratory

• Hormone assays: TSH, T3, T4, LH, FSH, Prolactin, PTH, Insulin, Cortisol
• Cardiac markers: Troponin I/T, CK-MB, BNP/NT-proBNP, Myoglobin
• Tumor markers: PSA, AFP, CEA, CA-125, CA 19-9, HCG
• Infectious disease: HIV Ag/Ab (4th generation), HBsAg, Anti-HCV, Anti-HBc, CMV IgM/IgG
• Autoimmune: ANA, anti-dsDNA, ANCA
• Allergy: Total IgE, specific IgE
• Drug monitoring: Digoxin, cyclosporine

• Sensitivity: 10⁻¹⁵ to 10⁻¹⁸ mol/L (attomolar range)
• Far superior to colorimetric ELISA (10⁻¹² mol/L)
• Wide dynamic range (6 log orders)

• ECL detection on Western blot membranes (replaced radioactive ³²P/¹²⁵I)

• Luminol spray at crime scenes (reacts with heme in blood)
• Environmental monitoring (bioluminescent bacterial biosensors)

• Non-radioactive Southern/Northern blots
• Acridinium-labeled probes for in-situ hybridization

Advantages Over Fluorescence

• No background autofluorescence
• No excitation light source needed
• Simpler optics
• Higher sensitivity

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Q23. MICROARRAY TECHNOLOGY AND APPLICATIONS

Definition

Principle

1. Extract RNA/DNA from specimen
2. Reverse transcribe RNA → cDNA (for expression arrays)
3. Label with fluorescent dyes (Cy3 = green; Cy5 = red)
4. Hybridize to microarray chip
5. Scan with laser scanner
6. Analyze intensity data

• Red spot = upregulated in tumor
• Green spot = downregulated in tumor
• Yellow spot = equal expression

Types of Microarrays

Applications in Pathology

• Molecular classification of breast cancer: PAM50 assay → Luminal A, Luminal B, HER2-enriched, Basal-like, Normal-like
• Oncotype DX (21-gene RT-PCR based): recurrence score in ER+ breast cancer
• MammaPrint (70-gene array, FDA-approved): prognosis in early breast cancer
• Gene expression profiling distinguishes tumor subtypes morphologically identical on H&E

• Chromosomal Microarray Analysis (CMA) - aCGH + SNP array: replaces conventional karyotyping for structural anomalies
• Detects copy number variants (CNVs) - deletions/duplications <5 Mb missed by karyotyping
• First-line test for intellectual disability, autism spectrum disorder, multiple congenital anomalies

• Gene expression response to drugs
• Identify drug targets
• Toxicity profiling

• Pathogen identification chips (resequencing arrays)
• Influenza subtyping microarray
• Antibiotic resistance gene detection

• Germinal center B-cell type vs Activated B-cell type in DLBCL
• Affects prognosis and treatment (R-CHOP response)

• Gene expression profiling in AML, ALL
• Identify high-risk molecular subgroups
• Response prediction

• Colorectal cancer molecular subtypes
• Lung cancer adenocarcinoma molecular classification

• Cytochrome P450 genotyping (CYP2D6, CYP2C19, CYP2C9)
• Warfarin dosing (VKORC1, CYP2C9)
• HLA typing (abacavir hypersensitivity, HLA-B*5701)

Tissue Microarray (TMA) - Special Type

• Cylindrical cores (0.6-2 mm) taken from multiple paraffin-embedded tumor blocks
• Assembled in a single recipient block
• Allows IHC/ISH on 100-1000 cases simultaneously on one slide
• Used for biomarker validation studies

Limitations of Microarrays

• Expensive (equipment + chips)
• Sophisticated bioinformatics required
• High background/noise; normalization critical
• Cannot detect novel mutations (only known sequences)
• mRNA may not reflect protein levels
• Superseded by NGS for many applications

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Q24. DENDRITIC CELLS: DISTRIBUTION AND THEIR DISEASES

Definition

Origin and Types

Distribution

• Skin: Langerhans cells in epidermis; dermal DCs in dermis
• Lymph nodes: paracortex (T-cell zones); afferent lymphatics carry DCs from tissues
• Spleen: marginal zone and T-cell areas
• Blood: ~0.5% of PBMCs (cDC1, cDC2, pDC)
• Mucosa: interstitial DCs in lamina propria (gut, lung, genital tract)
• Liver: mDCs in portal tracts and parenchyma
• Brain: microglia (brain-resident phagocytes, not true DCs)
• Thymus: DCs for central tolerance (negative selection)

Function

1. Capture antigens in peripheral tissues
2. Process antigens (peptide-MHC complexes)
3. Migrate to lymph nodes
4. Present to naive T cells → activate/tolerize
5. Provide co-stimulatory signals (CD80/86, CD40)
6. Produce cytokines (IL-12 → Th1; IL-4 → Th2; TGF-β+IL-6 → Th17; TGF-β → Treg)

Diseases of Dendritic Cells

• Clonal proliferation of CD1a+/CD207+ Langerhans-type cells
• BRAF V600E mutation in ~50% (driver mutation)
• Clinical: unifocal (bone - most common), multifocal unisystem, multisystem
• Pathology: Birbeck granules (tennis racquet-shaped) on EM; S-100+, CD1a+, CD207+
• Treatment: observation (unifocal) to chemotherapy (multisystem)

• Non-Langerhans histiocytosis (CD68+, CD1a-)
• BRAF V600E mutation common
• Systemic: bone, retroperitoneum, cardiovascular system
• Vemurafenib for BRAF V600E+

• Sinus histiocytosis with massive lymphadenopathy
• S-100+, CD68+, emperipolesis (lymphocytes inside histiocytes)

• Blastic plasmacytoid dendritic cell neoplasm
• Aggressive tumor, skin + bone marrow + lymph nodes
• CD123+, BDCA-2+, TCF4+; BCL2+
• Treatment: tagraxofusp (CD123-directed toxin fusion protein); allo-SCT

• Malignant tumor of FDCs
• Sites: lymph nodes, liver, spleen, abdomen
• CD21+, CD23+, CD35+; EBV+ in inflammatory variant
• Local recurrence common

• Rare; S-100+, CD1a-; lymph nodes

• pDC deficiency → increased viral susceptibility
• DC dysfunction in HIV infection

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Q25. CYTOKINES AND THEIR RECEPTORS IN T CELL DIFFERENTIATION

Introduction

T Helper Cell Differentiation

CD8+ T Cell Differentiation

• Naive CD8+ → Cytotoxic T lymphocyte (CTL): IL-2, IL-12, IFN-γ
• Produces: Perforin, Granzymes, IFN-γ, TNF
• Memory CD8+ T cells: IL-7, IL-15 (homeostatic maintenance)

Key Cytokine Receptors

• IL-2R: JAK1/3 → STAT5 → T cell proliferation, Treg survival
• IL-12R: JAK2/TYK2 → STAT4 → Th1 differentiation
• IL-4R: JAK1/3 → STAT6 → Th2 differentiation
• IL-6R: JAK1/2 + TYK2 → STAT3 → Th17 differentiation
• IFN-γR: JAK1/2 → STAT1 → macrophage activation

• Shared by IL-2, IL-4, IL-7, IL-9, IL-15, IL-21 receptors
• Mutations in γc → X-linked SCID (no T, NK cells)

• IL-12/IFN-γ inhibit Th2 differentiation
• IL-4/IL-13 inhibit Th1 differentiation
• IL-10 (Treg/Th2) suppresses macrophage activation and Th1/Th17
• IFN-γ inhibits Th17 differentiation

Disease Relevance

• Autoimmunity: excess Th1 (T1DM, RA) or Th17 (psoriasis, IBD, MS)
• Allergy/Asthma: excess Th2 → IL-4 (IgE switching), IL-5 (eosinophilia), IL-13 (mucus)
• Biologics: anti-TNF (RA), anti-IL-17 (psoriasis), anti-IL-23 (IBD), anti-IL-4Rα (dupilumab, asthma/eczema)
• Cytokine storm: COVID-19, CAR-T therapy - excess IL-6, IL-1β, TNF → tocilizumab/anakinra treatment

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Q26. IMMUNOLOGICAL ASPECTS OF TRANSPLANTATION

Types of Grafts

• Autograft: self-to-self (no rejection)
• Isograft: genetically identical (identical twins)
• Allograft: same species, different individual (most common)
• Xenograft: different species (pig-to-human)

MHC and Allorecognition

• HLA-A, B, C (Class I): on all nucleated cells; present peptides to CD8+ T cells
• HLA-DR, DQ, DP (Class II): on APCs; present to CD4+ T cells
• Best matching: DR > B > A reduces rejection risk

Types of Rejection

• Onset: Minutes to hours
• Mechanism: Preformed antibodies (anti-ABO, anti-HLA) → complement activation → thrombosis
• Pathology: Diffuse thrombosis, necrosis
• Prevention: ABO matching, crossmatch testing (CDC, ELISA, flow cytometry)
• Treatment: None; graft removal

• Onset: Days to months
• T cell-mediated (cellular) and/or antibody-mediated
• T cell-mediated: CD4+ and CD8+ T cells infiltrate graft; tubulitis, endarteriitis
• Antibody-mediated (AMR): Donor-specific antibodies (DSA) → complement → C4d deposition
• Treatment: High-dose steroids; ATG for steroid-resistant; plasmapheresis + IVIG for AMR

• Onset: Months to years
• Mechanism: Repeated low-grade immune injury + non-immune (CNI toxicity, hypertension)
• Pathology: Fibrosis, intimal hyperplasia, glomerulosclerosis, tubular atrophy
• DSA and indirect pathway important
• Treatment: Limited; optimize immunosuppression

• Donor T cells attack recipient tissues
• Acute GvHD (<100 days): skin, gut, liver
• Chronic GvHD (>100 days): autoimmune-like, fibrosis
• Treatment: Steroids, MMF, ruxolitinib

Pre-Transplant Workup

1. ABO blood group typing (essential)
2. HLA typing (recipient + donor): DR, B, A
3. Crossmatch tests: mix recipient serum + donor lymphocytes
   • CDC (complement-dependent cytotoxicity) crossmatch
   • Flow cytometry crossmatch (more sensitive)
   • Virtual crossmatch (DSA testing by Luminex)
4. PRA (Panel Reactive Antibody): % of HLA antigens in panel reactive with patient serum; >80% = highly sensitized

Immunosuppressive Therapy

1. Calcineurin inhibitors: Cyclosporine, Tacrolimus → block IL-2 production → inhibit T cell activation
2. Antiproliferatives: Azathioprine, Mycophenolate mofetil (MMF) → block T/B cell proliferation
3. mTOR inhibitors: Sirolimus, Everolimus → block IL-2 signaling
4. Corticosteroids: Anti-inflammatory; block cytokine transcription
5. Biologics: Basiliximab (anti-CD25), Belatacept (CTLA4-Ig, blocks costimulation), ATG, Rituximab (anti-CD20)

Tolerance in Transplantation

• Operational tolerance: graft accepted without immunosuppression
• Mechanisms: deletion (deletion of alloreactive clones), regulation (Tregs), anergy
• Clinical tolerance rare but goal of research

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Q27. GALLSTONES

Definition and Types

Pathogenesis of Cholesterol Stones - Triad

1. Supersaturation of bile with cholesterol (most important)
   • Increased hepatic cholesterol secretion (obesity, diet, estrogens, fibrates)
   • Decreased bile salt secretion
   • Decreased phospholipid secretion
2. Nucleation of cholesterol monohydrate crystals
   • Mucin glycoproteins, IgM - pro-nucleation
   • Apolipoproteins A-I, A-II - anti-nucleation
3. Gallbladder hypomotility - bile stasis allows crystal growth
   • Pregnancy, TPN, prolonged fasting, spinal cord injury, octreotide

Risk Factors - "5 Fs + more"

• Fat (obesity - most important modifiable risk)
• Female (estrogen: increases cholesterol secretion, reduces bile salt pool; oral contraceptives)
• Forty (>40 years)
• Fertile (multiparity, pregnancy - progesterone reduces gallbladder motility)
• Family history (genetic predisposition - ABC transporters, LITH genes)
• Additional: rapid weight loss, TPN, hemolytic anemias (pigment stones), Crohn's disease (decreased bile salt reabsorption), cirrhosis, biliary infections

Pathogenesis of Pigment Stones

• Black pigment: excess unconjugated bilirubin (hemolysis - sickle cell, hereditary spherocytosis, thalassemia) + cirrhosis; no infection
• Brown pigment: bacterial infection of bile (E. coli, Bacteroides) produces β-glucuronidase → unconjugated bilirubin precipitates with calcium; in bile ducts; recurrent pyogenic cholangitis

Complications

1. Biliary colic: transient obstruction of cystic duct
2. Acute cholecystitis: impacted stone in cystic duct + bacterial infection
3. Choledocholithiasis: stone in CBD → biliary obstruction + jaundice
4. Cholangitis: bacterial infection of bile ducts (Charcot's triad: RUQ pain, fever, jaundice; Reynolds' pentad adds hypotension + altered consciousness)
5. Acute pancreatitis: stone at ampulla of Vater
6. Hydrops / empyema of gallbladder
7. Mirizzi syndrome: large stone compresses CBD extrinsically
8. Gallstone ileus: stone erodes into bowel → intestinal obstruction
9. Carcinoma of gallbladder (long-standing cholesterol stones, porcelain GB)

Lab Investigations

• Bilirubin (direct/total), ALP, GGT, AST, ALT: obstructive pattern
• WBC, CRP: cholecystitis/cholangitis
• Amylase/lipase: pancreatitis
• Ultrasound: most sensitive (90-95% for gallbladder stones)
• MRCP/ERCP: CBD stones

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Q28. INTERNAL QUALITY CONTROL METHODS IN CLINICAL LABORATORY

Definition

Purpose

• Detect systematic and random errors
• Ensure analytical quality meets acceptance criteria
• Prevent reporting of erroneous results

Types of QC Materials

1. Commercial QC sera: lyophilized; 2-3 levels (low, normal, high); certified values
2. In-house QC: pooled patient sera; inexpensive; stability issue
3. Third-party QC: from company other than instrument/reagent manufacturer (preferred)

Methods of IQC

• Plot QC results against control limits
• Apply Westgard multirules

• Two levels of QC material on X and Y axes
• Each run plotted as a point
• Circular acceptance zone = random error
• Diagonal shift = systematic error
• Excellent for detecting run-to-run systematic shifts

• Plots cumulative deviation from target mean
• Excellent for detecting small systematic errors (trends) before they become obvious on LJ charts
• More sensitive than LJ for systematic error

• Uses average of consecutive patient results (especially for RBC indices like MCV)
• Bull's algorithm for CBCs
• Detects reagent/instrument drift using patient populations

• Same sample analyzed twice (different operators, instruments, or times)
• Assesses within-run or between-run precision

• Regularly compare results with reference laboratory or gold-standard method

• Automated system comparison of current patient result with previous result
• Flags implausible changes (e.g., Na drops 40 mEq/L overnight → likely sample error)
• Different from QC but contributes to pre-analytical error detection

Acceptance / Rejection Criteria

• σ = (TEa - Bias) / CV
• Where TEa = Total Allowable Error, Bias = systematic error, CV = imprecision
• σ ≥ 6: excellent (simple rules, fewer controls)
• σ 4-6: good
• σ < 4: poor (more QC, stricter rules needed)

Performance Indicators

• Precision: CV (coefficient of variation) = (SD/mean) × 100%; target <2-5% for most analytes
• Accuracy/Bias: difference from target value; detected by participation in EQAS
• Total Allowable Error (TEa): CLIA criteria; e.g., ±6% for glucose, ±10% for cholesterol

Key Point for Exam

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Q30. MUSCLE BIOPSY

Indications

1. Suspected muscular dystrophy (distinguish type)
2. Inflammatory myopathy (polymyositis, dermatomyositis, IBM)
3. Metabolic myopathy (mitochondrial, glycogen storage, lipid)
4. Congenital myopathy (structural abnormalities)
5. Vasculitis/polyarteritis affecting muscle
6. Neuropathic disorders (motor neuron, neuropathy - neurogenic atrophy)
7. Unexplained muscle weakness, elevated CK

Site Selection

• Moderately affected muscle (not normal, not end-stage)
• Common sites: vastus lateralis, biceps brachii, deltoid
• Guided by MRI or EMG findings
• Avoid site of previous EMG needle (cause focal changes)

Technique

• Open surgical biopsy preferred (larger sample, less artifact)
• Percutaneous needle biopsy (Bergstrom needle): less invasive, adequate for most
• Size: minimum 1×1 cm; ideally 2×1 cm
• Do NOT put in formalin - must go FRESH to lab (critical point)
• Clamp to prevent contraction artifact (optional, preferred)
• Transport on saline-moistened gauze, on ice

Processing

Stains Used in Muscle Biopsy

Normal Muscle Histology

• Uniform polygonal fibers
• Peripheral nuclei (central nuclei = pathological in adults except regenerating fibers)
• Type I (slow, oxidative): dark on ATPase pH 9.4; fatigue-resistant
• Type II (fast, glycolytic): light on ATPase pH 9.4; fatigue-prone
• Checkerboard pattern (type grouping = denervation)

Pathological Patterns

• Variation in fiber size, necrosis, regeneration, fibrosis
• DMD: absence of dystrophin by IHC; utrophin up-regulation on sarcolemma
• BMD: reduced/abnormal dystrophin
• LGMD: specific protein deficiency (dysferlin, calpain-3, etc.)

• Polymyositis: CD8+ T cell endomysial infiltrate; MHC-I upregulation on fibers
• Dermatomyositis: perifascicular atrophy; perivascular CD4+ T cells/B cells; MAC deposition on vessels
• IBM (Inclusion Body Myositis): rimmed vacuoles (MGT), congophilic inclusions; CD8+ inflammatory infiltrate

• Angulated small atrophic fibers (Type I and II)
• Type grouping (all Type I or all Type II clusters) = reinnervation
• Panfascicular atrophy: severe chronic denervation
• Nuclear clumps

• Glycogen storage: PAS+ subsarcolemmal deposits
• Mitochondrial: ragged red fibers (MGT), ragged blue (SDH), COX-negative fibers; electron microscopy = paracrystalline inclusions
• Lipid: Oil Red O+ vacuoles

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Q31. ROLE OF IHC IN DIAGNOSTIC PATHOLOGY

Principle of IHC

• Direct: labeled primary antibody (less sensitive)
• Indirect: labeled secondary antibody
• Avidin-biotin-complex (ABC)
• Polymer-based systems (most sensitive, no endogenous biotin issue): EnVision, DAKO REAL

Antigen Retrieval

• HIER (Heat-Induced Epitope Retrieval): microwave/pressure cooker in citrate buffer (pH 6) or EDTA (pH 9)
• PIER (Proteolytic-Induced): proteinase K, trypsin for some antigens

Applications

• Distinguish carcinoma (cytokeratins) from lymphoma (LCA/CD45) from melanoma (S-100, HMB-45) from sarcoma (vimentin)
• Primary vs metastatic origin (site-specific markers: TTF-1 = lung/thyroid; PSA = prostate; CDX2 = GI; GCDFP-15 = breast)

• ER, PR, HER2, Ki-67 in breast cancer (guides treatment)
• p16 in HPV-related squamous cell carcinoma (oropharynx, cervix)
• ALK in NSCLC (predicts response to crizotinib)
• PD-L1 (predicts response to immunotherapy)
• Microsatellite instability (MLH1, MSH2, MSH6, PMS2 loss)

• B-cell: CD20, CD79a, PAX5, BCL-2, BCL-6, CD10, MUM1
• T-cell: CD3, CD4, CD8, CD5, CD7, CD30, TIA-1, granzyme B
• Hodgkin vs Reed-Sternberg cells: CD15+, CD30+, PAX5 weak, CD20-, CD45-

• CMV: CMV-specific antibody (owl-eye inclusions confirmed)
• EBV: LMP1, EBER (ISH)
• H. pylori: anti-H. pylori antibody
• HPV (p16 surrogate marker)
• Fungi: antibodies against specific organisms

• Amyloid: Congo red + IHC for amyloid type (AA, AL, ATTR)
• Hemochromatosis: Perls iron stain + IHC
• Gaucher's disease: macrophages with PAS+ cytoplasm

• Synaptophysin, chromogranin, NSE (neuroendocrine)
• Site-specific hormones (insulin, glucagon, gastrin)

• Glial: GFAP (astrocyte), S-100 (Schwann cells, melanocytes)
• Neural: NF (neurofilament), synaptophysin, NSE
• IDH1/IDH2, ATRX, p53, MGMT methylation (glioma classification WHO 2021)

• Glomerular diseases: IgG, IgA, IgM, C3, C4d, fibrinogen (immunofluorescence)
• C4d positivity in peritubular capillaries: antibody-mediated rejection

• Positive tissue controls (every run)
• Negative controls (no primary antibody)
• Standardized protocols (ASCO/CAP guidelines for HER2, ER/PR)

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Q32. INDIRECT DNA DIAGNOSIS OF GENETIC DISEASES

Definition

Principle

• Uses Restriction Fragment Length Polymorphisms (RFLPs) or STR (Short Tandem Repeat) / microsatellite markers that are tightly linked to the disease gene
• Co-segregation of marker allele with disease allele in a family
• Requires informative family members (parents, affected child) for analysis

Technique (RFLP Analysis)

1. Extract DNA from family members
2. Digest with restriction enzyme that recognizes polymorphic site
3. Southern blot + probe hybridization
4. Determine allele size (RFLP pattern)
5. Track disease-linked allele through family

Requirements for Indirect Diagnosis

1. Informative family: both parents heterozygous for markers
2. Known affected relative (index case) to establish phase
3. Linkage disequilibrium or tight physical linkage (<1 cM)
4. Recombination as error source (if marker 1% recombinant, 1% false result)

Errors

• Recombination between marker and disease gene (false result)
• Incorrect phase assignment (no index case)
• Non-paternity
• New mutation not on tracked allele

Applications

1. Huntington's Disease (CAG repeat in HD gene; direct diagnosis now possible)
2. Duchenne Muscular Dystrophy (dystrophin gene very large - indirect used when no deletion identified)
3. Cystic Fibrosis (before comprehensive mutation panel; rare/novel mutations)
4. Hemophilia A and B (F8/F9 gene; intron 22 inversion in 40% - direct if known)
5. Familial Adenomatous Polyposis (APC gene - indirect with STRs)
6. Myotonic Dystrophy (DMPK gene expansion)
7. Alpha-thalassemia (difficult gene region)

Comparison: Direct vs Indirect

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Q33. APPLICATIONS OF PCR

Principle

Types of PCR

Clinical Applications of PCR

• HIV: viral load monitoring (RT-PCR); drug resistance genotyping
• HCV, HBV: viral load, genotyping, resistance
• Tuberculosis: GeneXpert MTB/RIF - diagnosis + rifampicin resistance in 2 hours
• Malaria: species identification, drug resistance (chloroquine, artemisinin)
• Chlamydia, Gonorrhea: NAAT (nucleic acid amplification tests) - most sensitive
• STI screening: multiplex NAAT for gonorrhea, chlamydia, trichomoniasis
• Meningitis panel: multiplex PCR (FilmArray) - bacteria + virus + fungi from CSF
• Respiratory panel: influenza A/B, RSV, adenovirus, rhinovirus, coronavirus
• COVID-19: SARS-CoV-2 detection (gold standard)
• CMV, EBV: quantitative PCR for immunocompromised patients
• HSV encephalitis: CSF PCR (gold standard, sensitivity >95%)

• BCR-ABL in CML (quantitative - MRD monitoring)
• EGFR mutations (lung cancer): exons 18-21
• KRAS, NRAS, BRAF (colorectal, melanoma)
• PML-RARA in APL
• JAK2 V617F in myeloproliferative neoplasms
• BRCA1/BRCA2 germline testing
• MLH1, MSH2, MSH6, PMS2 (Lynch syndrome)
• NPM1, FLT3-ITD in AML
• IDH1/IDH2 in glioma, AML
• PDGFRA/KIT in GIST (imatinib sensitivity)

• Cystic fibrosis (CFTR mutations)
• Sickle cell (ARMS-PCR for HbS)
• Alpha/beta-thalassemia (deletion multiplex PCR)
• DMD deletions (multiplex PCR of 19 exons)
• Fragile X (repeat expansion sizing)
• Prenatal diagnosis: from CVS/amniocytes

• DNA fingerprinting (STR profiling)
• Paternity testing
• Crime scene identification
• Mass disaster victim identification

• HLA typing (sequence-specific PCR, SSP)

• GMO detection in food
• Water/air pathogen surveillance

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Q34. SEROLOGICAL TESTS IN DIAGNOSIS OF MALIGNANCIES

Additional Serological Methods

• Types M protein in myeloma (IgG, IgA, IgM, IgD, IgE + kappa/lambda)
• More sensitive than SPEP for small M proteins

• Serum free light chain assay
• κ/λ ratio >3.1 or <0.26 = abnormal
• Highly sensitive for multiple myeloma, AL amyloidosis, MGUS
• Monitor response to myeloma treatment

• Immunophenotyping leukemia/lymphoma
• CD markers help classify leukemia (B-ALL: CD19, CD10, TdT; T-ALL: CD3, CD7; AML: CD33, CD13, MPO)
• MRD detection

• Cold agglutinin hemolytic anemia: associated with lymphoma, Waldenström's

• Myeloma staging and prognosis (ISS staging)
• Also elevated in lymphoma, leukemia

• Older technique; replaced by IFE

• Free light chains in urine (heat test or SPEP/IFE on concentrated urine)
• Multiple myeloma (light-chain disease)

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Q37 & Q42. CALCIUM METABOLISM IN HEALTH AND DISEASE

Normal Calcium Metabolism

• Ionized (free): 45-50%; physiologically active; regulated; 1.1-1.4 mmol/L
• Protein-bound: 40% (mainly albumin); biologically inactive
• Complexed: 10% (with citrate, phosphate, bicarbonate)

Regulation of Calcium

• Low ionized Ca → PTG sensors (CaSR) → ↑PTH → ↑Ca
• High ionized Ca → ↓PTH, ↑calcitonin → ↓Ca

Absorption

• Duodenum and proximal jejunum
• Active transport (via TRPV6, calbindin, PMCA1): stimulated by 1,25(OH)₂D₃
• Passive paracellular: concentration-dependent
• Normal absorption: 30-40% of intake; increases in deficiency

Renal Handling

• Freely filtered; 99% reabsorbed
• Proximal tubule: 65% (passive, with Na)
• Thick ascending limb: 25% (paracellular; reduced by furosemide)
• Distal tubule: 5-10% (active, PTH-dependent, TRPV5 channel)
• Collecting duct: 1%
• PTH: ↑Ca reabsorption in DCT
• Furosemide: ↑Ca excretion (used in hypercalcemia)
• Thiazide diuretics: ↑Ca reabsorption (used in Ca-oxalate stones, hypercalciuria)

Hypercalcemia

1. Hyperparathyroidism (primary: adenoma 85%, hyperplasia, carcinoma)
2. Malignancy (most common cause in hospitalized patients):
   • PTHrP secretion (solid tumors: lung, breast, squamous)
   • Osteolytic metastases (breast, myeloma, lymphoma)
   • 1,25(OH)₂D production (lymphomas, granulomas)
3. Granulomatous diseases: sarcoidosis, TB, fungal (excess 1,25(OH)₂D production by macrophages)
4. Vitamin D toxicity
5. Milk-alkali syndrome (excessive Ca + antacid)
6. Thiazide diuretics (reduced Ca excretion)
7. Immobilization (increased bone resorption)
8. FHH (Familial Hypocalciuric Hypercalcemia): CaSR mutation; benign
9. Hypothyroidism, Addison's, Paget's disease

• Moans: N/V, constipation, anorexia
• Groans: fatigue, weakness
• Stones: nephrolithiasis (calcium oxalate/phosphate), nephrocalcinosis
• Bones: bone pain, pathological fractures, subperiosteal resorption
• Psychic: depression, confusion, coma (severe)
• Short QT interval on ECG

• IV fluids (normal saline) - first step always
• Furosemide - enhances Ca excretion
• Bisphosphonates (zoledronate): inhibit osteoclasts; for malignancy
• Denosumab: anti-RANKL; resistant cases
• Calcitonin: rapid onset, tachyphylaxis
• Dialysis: severe, renal failure
• Glucocorticoids: sarcoidosis, vitamin D toxicity
• Surgery: for primary hyperparathyroidism

Hypocalcemia

1. Hypoparathyroidism (post-thyroidectomy, autoimmune, DiGeorge)
2. Pseudohypoparathyroidism (end-organ resistance to PTH)
3. Vitamin D deficiency/malabsorption
4. Chronic renal failure (↓1α-hydroxylase + hyperphosphatemia)
5. Hypomagnesemia (impairs PTH secretion and action)
6. Pancreatitis (saponification)
7. Hungry bone syndrome (post-parathyroidectomy)
8. Alkalosis (↓ionized Ca with normal total Ca)
9. Massive transfusion (citrate binds Ca)

• Perioral numbness, tingling
• Chvostek sign: tapping facial nerve → facial muscle twitch
• Trousseau sign: inflate BP cuff → carpal spasm (carpopedal spasm)
• Tetany, seizures, laryngospasm
• Prolonged QT interval (risk of Torsades de Pointes)
• Cataracts, papilledema (chronic)

• IV calcium gluconate (emergency): 10 mL of 10% = 90 mg elemental Ca
• Oral calcium carbonate/citrate (maintenance)
• Active vitamin D (calcitriol) for hypoparathyroidism
• Magnesium correction if deficient

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Q41. COPPER METABOLISM AND CERULOPLASMIN

Copper Metabolism

Absorption

• Small intestine (duodenum and proximal jejunum)
• Copper transporter 1 (CTR1) on enterocytes
• Metallothionein: intracellular copper storage protein
• Prevented by high zinc (induces metallothionein → traps Cu in enterocytes)

Transport

1. Albumin + histidine: carry ~15% of plasma copper (free/loosely bound)
2. Ceruloplasmin: carries ~65-70% of plasma copper (tightly bound)
3. Macroglobulin: small amount

Ceruloplasmin

• Synthesis: Liver (hepatocytes)
• Function:
  • Copper transport
  • Ferroxidase activity: oxidizes Fe²⁺ → Fe³⁺ (essential for transferrin loading → iron metabolism)
  • Antioxidant (scavenges superoxide radicals)
  • Acute phase reactant (levels rise in inflammation, pregnancy, estrogens)
• Normal levels: 20-35 mg/dL (200-350 mg/L)

Excretion

• Biliary excretion (primary route): 80-90%
• Only trace in urine (normally <50 μg/24h)

Wilson's Disease (Hepatolenticular Degeneration)

• Autosomal recessive: mutation in ATP7B gene (chromosome 13q14.3)
• ATP7B = P-type ATPase transporter; normally:
  • Incorporates Cu into ceruloplasmin in Golgi
  • Excretes Cu into bile
• In Wilson's: Cu accumulates in liver, brain (lenticular nucleus), cornea, kidneys, etc.

• Serum ceruloplasmin: LOW (<20 mg/dL) - because apoceruloplasmin not loaded with Cu
• Serum copper: low (paradox - most Cu is non-ceruloplasmin-bound)
• Urine copper (24h): HIGH (>100 μg/day; >250 μg/day in symptomatic)
• Liver copper: HIGH (>250 μg/g dry weight); gold standard
• Kayser-Fleischer (KF) rings: golden-brown ring at Descemet's membrane (slit-lamp)
• Coombs-negative hemolytic anemia (due to Cu release from liver)
• Liver biopsy: hepatitis, cirrhosis, steatosis; rhodanine/orcein stain for Cu

• D-penicillamine (chelation) or Trientine (chelation; better tolerated)
• Zinc (blocks intestinal Cu absorption)
• Low copper diet
• Liver transplant (if liver failure)

Menkes Disease (Kinky Hair Disease)

• X-linked recessive: ATP7A gene mutation
• Failure of intestinal Cu absorption and transport
• Copper accumulates in intestinal cells; systemic Cu deficiency
• Features: kinky depigmented hair, intellectual disability, progressive neurodegeneration, arterial tortuosity
• Low serum Cu, low ceruloplasmin
• Treatment: copper histidine injections

Other Causes of Abnormal Ceruloplasmin

• Elevated: Pregnancy, estrogens (OCP), rheumatoid arthritis, infections, liver disease (acute), primary biliary cholangitis
• Decreased: Wilson's, Menkes, severe liver failure, nephrotic syndrome (protein loss), malnutrition, aceruloplasminemia (rare genetic)

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Q43. ACID-BASE BALANCE

Fundamental Concepts

• pH = -log[H⁺]; normal serum pH = 7.35-7.45
• Acidemia: pH <7.35; Alkalemia: pH >7.45
• Henderson-Hasselbalch equation: pH = pKa + log([HCO₃⁻] / [0.03 × PaCO₂])
• Normal values: PaCO₂ = 35-45 mmHg; HCO₃⁻ = 22-26 mEq/L

Buffer Systems

1. Bicarbonate-carbonic acid (most important in plasma): HCO₃⁻/H₂CO₃
2. Phosphate: H₂PO₄⁻/HPO₄²⁻ (important in urine and intracellular)
3. Protein (including hemoglobin): imidazole groups
4. Bone carbonate: long-term buffering

Regulation

• Respiratory: rapid (minutes); lungs regulate CO₂
  • Acidosis → ↑ventilation → ↓PaCO₂ → ↑pH
• Renal: slow (hours-days); regulates HCO₃⁻
  • HCO₃⁻ reabsorption (proximal tubule - 85%)
  • NH₄⁺ excretion (proximal + distal)
  • Titratable acid (H₂PO₄⁻, distal tubule)
  • New HCO₃⁻ generation

Four Primary Disorders

• Volume-depleted (saline-responsive, urine Cl <15): vomiting, nasogastric suction, diuretics, diarrhea with Cl loss
• Volume-expanded (saline-resistant, urine Cl >15): Conn's syndrome, Cushing's, Bartter's, Gitelman's, licorice

• Acute: HCO₃⁻ increases 1 mEq/L per 10 mmHg rise in PaCO₂
• Chronic: HCO₃⁻ increases 3.5 mEq/L per 10 mmHg rise in PaCO₂

• Acute: HCO₃⁻ decreases 2 mEq/L per 10 mmHg fall in PaCO₂
• Chronic: HCO₃⁻ decreases 5 mEq/L per 10 mmHg fall in PaCO₂

Systematic Approach to ABG Analysis

1. Look at pH: acidemia (<7.35) or alkalemia (>7.45)
2. Primary disorder: check PaCO₂ and HCO₃⁻
3. Expected compensation: use formulas above
4. If compensation is appropriate → simple disorder
5. If not → mixed disorder
6. In metabolic acidosis: calculate anion gap
7. If high AG: calculate delta gap = (AG - 12) / (24 - HCO₃⁻); if >1 = also metabolic alkalosis; if <1 = also normal AG metabolic acidosis

Approach Table

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COMPLETE INDEX OF ANSWERS

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EXAM TIPS FOR APED FORMAT

1. A (Answer/Define): Begin with a crisp 1-2 sentence definition or introduction
2. P (Points/Classification): Immediately give a systematic classification or list of types
3. E (Elaborate): Expand each point with mechanisms, examples, clinical significance
4. D (Diagrams/Tables): Use tables wherever comparison is needed; draw simple flow diagrams when writing by hand