PPD infectious

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tuberculin skin test PPD interpretation

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tuberculin skin test PPD Mantoux induration reading

This clinical photograph displays a Mantoux tuberculin skin test site on the volar aspect of a human forearm, 72 hours post-intradermal injection of purified protein derivative (PPD). The visual findings demonstrate a positive reaction characterized by a central, well-defined zone of induration exhibiting a reddish-purple, dusky hue. Surrounding the induration is a peripheral ring of lighter pink erythema. The lesion is roughly circular in morphology, measuring approximately 24 mm in diameter. The surrounding skin appears otherwise normal with standard follicular distribution. This image is a classic educational representation used in infectious disease and pulmonology to illustrate delayed-type hypersensitivity (Type IV) reactions and screening for Mycobacterium tuberculosis infection. Key diagnostic features highlighted include the palpable firmness (induration) and the significant size threshold indicating a positive result in clinical diagnostic protocols.

This clinical photograph displays a positive Mantoux tuberculin skin test on the volar aspect of a patient's forearm. The visual hallmark is a central, well-demarcated area of induration, appearing as a raised, firm, and palpable plaque. The indurated center exhibits a slightly lighter, yellowish-tan coloration with a textured, peau d'orange appearance compared to the surrounding skin. Encircling this central induration is a broad, poorly defined halo of erythema (redness). The reaction site is roughly circular, and a small central puncture mark from the intradermal injection is visible. In the clinical context provided, this measure of 28 mm represents a strongly positive reaction, indicating a delayed-type hypersensitivity response to Purified Protein Derivative (PPD). Such a robust reaction is highly suggestive of infection with Mycobacterium tuberculosis and, in this specific case, correlates with systemic findings of ocular and pulmonary tuberculosis.

This clinical photograph displays a positive Tuberculin Skin Test (Mantoux test) on the forearm of a patient. The image shows a well-defined, raised erythematous plaque characterizing a strongly reactive 19 mm PPD (purified protein derivative) result. The lesion is primarily a reddish-pink circular area of induration, exhibiting a slightly bumpy, textured surface with fine papular elevations. The surrounding skin shows mild peripheral erythema that fades into the normal skin tone. This visual represents a delayed-type hypersensitivity reaction (Type IV), indicative of current or past infection with Mycobacterium tuberculosis. The educational focus is on the clinical assessment of induration rather than just erythema to determine a positive diagnostic result in tuberculosis screening.

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Here is a comprehensive overview of the PPD (Purified Protein Derivative) test in the context of infectious disease - particularly tuberculosis.

PPD (Tuberculin Skin Test / Mantoux Test) - Infectious Disease

What Is PPD?

The Purified Protein Derivative (PPD) test - also called the Mantoux tuberculin skin test - detects delayed-type hypersensitivity (Type IV) to Mycobacterium tuberculosis antigens. It identifies individuals who have been infected (latent or active) but does NOT differentiate between latent infection and active disease.

Robbins & Kumar Basic Pathology and Robbins, Cotran & Kumar Pathologic Basis of Disease both confirm: A positive tuberculin test "signifies T cell-mediated immunity to mycobacterial antigens but does not differentiate between infection and active disease."

How It Works - Mechanism

Intracutaneous injection of 0.1 mL of PPD (5 tuberculin units) into the volar forearm
A Type IV (delayed-type) hypersensitivity reaction is triggered by sensitized T lymphocytes
Read at 48-72 hours - measure the induration (not erythema/redness)
Use a ruler or ballpoint pen technique to measure the raised, palpable area in millimeters

Positive Mantoux test (24 mm) showing central induration with surrounding erythema

A positive Mantoux test at 72 hours - note the central indurated (palpably raised) area rather than just the surrounding erythema.

Interpretation - Positivity Thresholds

Induration	Group
≥ 5 mm	HIV-positive individuals; recent close contacts of active TB; fibrotic changes on CXR consistent with old TB; organ transplant recipients; immunosuppressed patients (e.g., on ≥15 mg/day prednisone)
≥ 10 mm	Recent immigrants from high-prevalence countries (<5 years); IV drug users; residents/employees of high-risk congregate settings (prisons, nursing homes, hospitals); mycobacteriology lab personnel; children <4 years; those with medical risk factors (diabetes, silicosis, CKD, malignancy, low body weight)
≥ 15 mm	Any person with no known risk factors (general population screening)

False Negatives (Anergy)

The PPD can be falsely negative in several conditions - this is called anergy:

HIV infection / AIDS (especially low CD4 count)
Active overwhelming TB disease itself (paradoxically)
Malnutrition
Sarcoidosis
Hodgkin lymphoma
Recent viral infections (measles, varicella, influenza)
Corticosteroid or immunosuppressive therapy
Very young age (<6 months)

As noted in Robbins, Cotran & Kumar: "notably overwhelming active tuberculous disease" is itself a cause of false-negative reactions.

False Positives

BCG vaccination (attenuated M. bovis) - common in many countries; can cause false positives, though reactions >15 mm are unlikely to be due to BCG alone
Nontuberculous mycobacteria (NTM) infections - atypical mycobacteria (e.g., M. avium, M. kansasii) can cross-react
Incorrect technique (measuring erythema instead of induration)

PPD vs. IGRA (Interferon-Gamma Release Assay)

Feature	PPD (TST)	IGRA (QuantiFERON, T-SPOT)
Method	Intradermal injection, read at 48-72h	In vitro blood test
BCG interference	Yes - can cause false positive	Minimal/no
NTM interference	Yes	Less
Requires 2 visits	Yes	No
Anergy affected	Yes	Yes
Differentiates latent vs. active	No	No
Cost	Lower	Higher

IGRAs are preferred in BCG-vaccinated individuals and those unlikely to return for reading. IGRAs use M. tuberculosis-specific antigens (ESAT-6, CFP-10) absent from BCG and most NTM.

Clinical Significance

A positive PPD in a previously negative individual ("tuberculin conversion") indicates new infection - 3-4% will develop active TB in the first year after conversion
All newly positive individuals should receive clinical evaluation and chest X-ray
Latent TB infection (LTBI) treatment is indicated for positive tests in appropriate risk groups (typically 9 months isoniazid, or shorter rifamycin-based regimens)
In pre-biologic therapy screening (e.g., anti-TNF agents like infliximab), PPD or IGRA is mandated before initiation - as noted in Firestein & Kelley's Textbook of Rheumatology

Epidemiology

~80% of the population in certain Asian and African countries is tuberculin positive
In 2019, approximately 5% of the U.S. population was positive
An estimated 13 million cases of latent tuberculosis exist in the United States as of 2019
TB remains the most common cause of death from a single endemic infectious agent worldwide (WHO) - 1.3 million deaths and 5.8 million new cases in 2021

Key sources:

Robbins & Kumar Basic Pathology (9780323790185)
Robbins, Cotran & Kumar Pathologic Basis of Disease (9780443264528)
Medical Microbiology 9e (9780323673228)

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Gram stain bacteria purple red microscopy

This light microscopy image demonstrates a Gram stain of an excised clinical sample, typically used in microbiology for diagnostic identification. The central focus shows a dense cluster of Gram-variable filamentous rods, characteristic of Actinomyces species. These organisms appear as dark, elongated, branching, thread-like structures. Some filaments exhibit a beaded appearance, staining more intensely (Gram-positive/purple) or less intensely (Gram-negative/pink) along their length. The background consists of host cellular debris and inflammatory cells, which are counterstained pink/red with safranin. These background elements include various eukaryotic cells and likely polymorphonuclear leukocytes. This visual is highly representative of Actinomycosis, demonstrating the classic 'sulfur granule' or 'tangled mass' morphology often seen in abscess aspirates or tissue samples. It serves as a critical educational tool for distinguishing filamentous bacteria from standard cocci or bacilli and highlights the importance of Gram stain variability in clinical diagnostics.

This composite diagnostic image presents two light microscopy views of pleural fluid highlighting the microbiological identification of Nocardia species. Panel (a) shows a Gram stain at high magnification, demonstrating Gram-positive (purple-stained), thin, beaded, and branching filamentous bacteria. Panel (b) illustrates a modified Ziehl-Neelsen (ZN) stain of the same clinical specimen. The bacteria exhibit weak acid-fast properties, characterized by pink-to-red filamentous structures that retain the primary stain against a light blue counterstained background. Arrows in both panels indicate the characteristic filamentous and branching morphology. This combination of Gram-positive branching filaments and partial acid-fastness is a key diagnostic feature used to distinguish Nocardia from other filamentous bacteria like Actinomyces. These findings are clinically significant in diagnosing thoracic nocardiosis in immunocompromised patients or those with pre-existing pulmonary disease.

Your image is a Persian (Farsi) checklist of essential procedures for an infectious disease ward. The two columns are:

پروسیجرهای ضروری = Essential Procedures
نحوه ی آموزش (کیس/فیلم...) = Method of Training (Case/Film/...) - for competency sign-off

Here is a full clinical guide to each of the 9 procedures listed:

Essential Procedures - Infectious Disease Ward (پروسیجرهای ضروری)

1. PPD (پی‌پی‌دی)

(Already covered in detail above)

The Mantoux tuberculin skin test - 0.1 mL intradermal injection of purified protein derivative read at 48-72 hours. Measures induration (not erythema). Thresholds: ≥5 mm (immunocompromised), ≥10 mm (high-risk), ≥15 mm (general population). Essential in TB screening, pre-biologic therapy workup, and contact investigation.

2. تهیه لام خون محیطی - Peripheral Blood Smear Preparation

Purpose in the infectious ward: Detect malaria parasites, identify morphological changes in sepsis (toxic granulation, Döhle bodies, left shift), assess for hemolytic anemia in infections, diagnose babesiosis, relapsing fever (Borrelia), trypanosomiasis.

Technique:

Place a small drop of fresh blood (EDTA or fingerstick) near one end of a clean glass slide
Place a spreader slide at a 30-45° angle, back it into the drop, and push forward in one smooth motion
The smear should be thin enough that RBCs are in a single layer at the feathered edge
Air-dry immediately - do NOT blow or heat-fix
Stain with Wright-Giemsa or Field stain (for malaria, use thick and thin smears)
Read under 100x oil immersion

Key findings in infection:

Finding	Significance
Ring forms in RBCs	Malaria (P. falciparum, P. vivax, etc.)
Toxic granulation, band forms	Bacterial sepsis
Atypical lymphocytes	EBV (mononucleosis), CMV
Schistocytes	Thrombotic microangiopathy (HUS/TTP)
Intraerythrocytic rings/Maltese cross	Babesiosis

3. رنگ آمیزی گرم - Gram Staining

Purpose: Classify bacteria as Gram-positive (purple) or Gram-negative (red/pink) and identify morphology (cocci, rods, chains). Guides empiric antibiotic choice within minutes.

Procedure (from Jawetz Medical Microbiology):

Crystal violet - flood the smear, wait 1 minute → all bacteria turn purple
Gram's iodine - apply as mordant, 1 minute → forms crystal violet-iodine complex
Decolorizer (95% ethanol or acetone-alcohol) - 5-10 seconds → Gram-negative cells lose purple; Gram-positive cells retain it
Safranin (counterstain) - 1 minute → Gram-negative cells turn red/pink

Interpretation:

Result	Color	Examples
Gram-positive cocci in clusters	Purple	S. aureus
Gram-positive cocci in chains	Purple	Streptococcus spp.
Gram-negative diplococci	Pink	N. meningitidis, N. gonorrhoeae
Gram-negative rods	Pink	E. coli, Klebsiella, Pseudomonas
Gram-positive rods	Purple	Listeria, Clostridium

The acid-fast stain (Ziehl-Neelsen) is a variation used when mycobacteria are suspected - carbolfuchsin with acid-alcohol decolorization; mycobacteria appear red against a blue counterstain.

Gram stain demonstrating filamentous bacteria with purple (Gram-positive) and pink (Gram-negative) morphology

4. احتیاطات استاندارد و ایزولاسیون - Standard Precautions and Isolation

Standard precautions apply to ALL patients regardless of diagnosis. They include:

Hand hygiene - soap and water (for C. difficile and norovirus) or alcohol-based hand rub for most pathogens
PPE - gloves for contact with blood/body fluids; mask, gown, eye protection when splash risk exists
Safe needle handling - never recap; use safety devices; sharps containers replaced at 2/3 full
Respiratory hygiene / cough etiquette
Aseptic technique for procedures

Isolation categories for infectious wards:

Type	Route	PPE Required	Examples
Contact	Touch/fomites	Gloves + gown	MRSA, VRE, C. diff, scabies, impetigo
Droplet	Large droplets (>5 µm)	Surgical mask + gloves	Influenza, meningococcal meningitis, mumps, pertussis
Airborne	Small droplets (<5 µm)	N95 respirator + negative-pressure room	TB, measles, varicella, SARS-CoV-2 (aerosol-generating procedures)
Protective / Reverse	Protect immunocompromised patient	Positive-pressure room, HEPA filtration	Neutropenic patients, BMT recipients

Skin prep for blood culture collection: 2% chlorhexidine gluconate in 70% isopropyl alcohol is preferred over iodine for adult patients - Red Book (AAP).

5. گرفتن نمونه کشت خون - Obtaining Blood Culture Sample

Purpose: Diagnose bacteremia, fungemia, and sepsis. The only definitive way to identify the causative organism and guide targeted therapy.

Technique:

Gather 2 sets of bottles (each set = 1 aerobic + 1 anaerobic) from 2 separate venipuncture sites (reduces contamination interpretation)
Skin antisepsis: Clean with 2% chlorhexidine-alcohol (allow to dry 30 seconds) or 2% tincture of iodine
Draw 8-10 mL per bottle in adults (higher volume improves yield - each 1 mL increase raises yield ~3%)
Inoculate the anaerobic bottle first when using a butterfly needle (removes air from line), aerobic first with direct syringe
Time cultures before antibiotics if possible - sensitivity drops significantly after even one antibiotic dose
Label with time, site, and bottle number
Transport to lab within 2 hours

Yield considerations:

2 sets detect ~80-90% of bacteremia episodes
3 sets detect ~96%
Common contaminants: CoNS (coagulase-negative staphylococci), Bacillus, diphtheroids - single positive set usually indicates contamination

6. گرفتن نمونه کشت حلق - Obtaining Throat Culture Sample

Purpose: Diagnose Group A Streptococcus (GAS) pharyngitis, diphtheria, N. gonorrhoeae (in sexually active patients), Candida, and bacterial carriers.

Technique:

Have the patient open mouth wide, use a tongue depressor to depress the tongue
Use a sterile Dacron (not cotton) swab
Swab both tonsillar pillars and the posterior pharynx - specifically any areas of exudate, erythema, or membrane
Avoid touching the tongue, teeth, or lips - these contaminate the specimen
Place swab into appropriate transport medium immediately
For GAS, rapid antigen detection tests (RADT) give results in minutes; culture is the gold standard but takes 24-48h
For diphtheria, use specific media (Loeffler's serum, tellurite agar) and alert lab

Important: For suspected epiglottitis - do NOT perform throat swab; it may trigger laryngospasm. Proceed to airway management.

7. نمونه از زخم پوستی - Skin Wound Sampling

Purpose: Identify causative organism in cellulitis, wound infection, abscess, necrotizing fasciitis, infected ulcers (diabetic, pressure), leishmaniasis, and cutaneous TB.

Technique depends on wound type:

Wound Type	Preferred Method
Abscess / pustule	Aspirate pus with needle/syringe before opening; send for C&S + Gram stain
Open wound / ulcer	Cleanse wound first with saline; use Levine technique - swab the wound base with firm rotation over 1 cm² area for 5 seconds
Tissue biopsy	Best for deep infections, leishmaniasis, necrotizing fasciitis - punch biopsy or surgical sample
Blister / vesicle	Unroof and swab base (Tzanck smear + viral culture for HSV/VZV)
Sinus tract	Probe and culture the deepest accessible area, not the opening

Always send for:

Gram stain + aerobic/anaerobic culture
If actinomycosis or mycobacterium suspected: acid-fast stain and fungal culture
If leishmaniasis suspected: smear + culture on NNN media

8. لومبار پونکسیون - Lumbar Puncture (Spinal Tap)

Purpose: Diagnose bacterial/viral/fungal meningitis, encephalitis, subarachnoid hemorrhage, carcinomatous meningitis, CNS TB.

Procedure (from Neuroanatomy through Clinical Cases):

Position: Lateral decubitus (fetal) position with maximal spine flexion, OR seated leaning forward - lateral is preferred for pressure measurement
Landmark: L4-L5 interspace (line between the posterior iliac crests = level of L4 spinous process) - this is BELOW the spinal cord terminus (conus at L1-L2)
Sterile technique: full aseptic prep (chlorhexidine + drapes), sterile gloves
Local anesthesia: 1-2% lidocaine subcutaneously
Insert spinal needle (20-22G) with stylet in the midline, angled slightly toward the umbilicus
Feel a "pop" as the needle enters the subarachnoid space
Measure opening pressure with a manometer (normal: <20 cm H₂O)
Collect CSF into 4 numbered tubes sequentially (tubes 1&4 for cell count, tube 2 for chemistry, tube 3 for microbiology)

CSF interpretation in meningitis:

Finding	Bacterial	Viral	TB/Fungal
Appearance	Turbid/cloudy	Clear	Clear/slightly turbid
WBC	>1000/µL, neutrophils	10-1000/µL, lymphocytes	100-500/µL, lymphocytes
Protein	Very high (>100 mg/dL)	Normal/mildly raised	High (100-500 mg/dL)
Glucose	Very low (<45 mg/dL)	Normal	Low
Gram stain	Often positive	Negative	Negative (AFB in TB)

Contraindications: Raised ICP with mass lesion (herniation risk - get CT first), coagulopathy (INR >1.5, platelets <50,000), overlying skin infection, suspected spinal epidural abscess.

Complication: Post-LP headache (1-70% incidence) - positional, worsens upright, relieved lying down. Managed conservatively or with epidural blood patch.

9. تفسیر آزمایشات - Interpretation of Lab Tests

This is the overarching competency that integrates all of the above. In the infectious ward, key lab panels include:

Panel	Key Interpretation Points
CBC	WBC with differential - neutrophilia (bacterial), lymphocytosis (viral), eosinophilia (parasites/fungi), neutropenia (risk for opportunistic infections)
CRP / ESR / Procalcitonin	PCT >0.5 ng/mL favors bacterial infection; PCT-guided therapy can reduce antibiotic duration
Blood cultures	Identify organism + susceptibilities; 2 positive sets = true bacteremia; single set CoNS = likely contaminant
LFTs / Renal function	Drug dosing adjustments; aminoglycosides, vancomycin, acyclovir, fluconazole all require renal dose adjustment
Gram stain & culture	Correlate morphology (Gram stain) with colony type and sensitivities
Serologies	Acute vs. convalescent titers; IgM = acute infection; IgG = past exposure/immunity
CSF analysis	See LP table above
HIV serology / viral loads	4th generation Ag/Ab test detects both p24 antigen and antibody; viral load guides treatment and infectivity

Sources:

Jawetz, Melnick & Adelberg's Medical Microbiology 28e - Gram staining
Neuroanatomy through Clinical Cases 3e - Lumbar puncture
Red Book 2021 (AAP) - Standard precautions, blood culture aseptic technique
Robbins & Kumar Basic Pathology - PPD/tuberculin skin test

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lumbar puncture spinal needle CSF collection technique positioning

This clinical procedural photograph illustrates a subarachnoid puncture, commonly referred to as a lumbar puncture, being performed for cerebrospinal fluid (CSF) collection or drainage. The image shows a spinal needle inserted into the lumbar region of a patient, specifically at the L2-L3 interspace. The procedural site is prepared with sterile blue surgical drapes. A key clinical finding is the visualization of clear, colorless fluid (CSF) dripping from the hub of the spinal needle into a sterile collection container, confirming successful entry into the subarachnoid space. This visual evidence of 'free-flow' is critical for diagnostic sampling and therapeutic pressure management. The photograph demonstrates proper aseptic technique and the lateral approach for accessing the lumbar cistern. It serves as an educational tool for medical students and clinicians to recognize the appearance of CSF during neurosurgical or neurological procedures, highlighting the correct anatomical positioning and procedural outcomes in a clinical setting.

A clinical photograph depicting a healthcare professional performing a lumbar puncture (spinal tap) on a patient in a clinical setting. The patient is positioned in a lateral decubitus posture, lying on their side with the spine flexed and knees drawn toward the chest to increase the interspinous space. The healthcare worker, wearing a white lab coat and sterile gloves, is shown inserting a spinal needle into the lumbar region, specifically targeting the subarachnoid space to collect cerebrospinal fluid (CSF). The visual captures the precise manual technique required for this invasive procedure. Contextually, this diagnostic maneuver is illustrated here as a critical step in staging African Sleeping Sickness (Human African Trypanosomiasis) to detect central nervous system involvement. This image serves as a teaching tool for neuro-diagnostic procedures and clinical manifestations of tropical diseases in resource-limited environments.

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blood culture bottles aerobic anaerobic collection venipuncture

This clinical photograph captures a venipuncture procedure for blood collection, specifically from the brachial vein in the antecubital fossa of a patient's arm. The setup features a winged infusion set (butterfly needle) with a green safety shield, which is inserted into the vein. A flexible plastic extension tube connects the needle to a vacuum collection tube. The collection tube has a red cap, indicating it is likely a plain serum tube without anticoagulants, and is seen partially filled with dark venous blood. The patient's arm is positioned on a green medical cushion, with a practitioner's hand visible providing stabilization. This procedural image demonstrates the initial step in obtaining blood for Platelet-Rich Fibrin (PRF) preparation, highlighting the medical specialty of oral and maxillofacial surgery or regenerative medicine. The educational focus is on the aseptic technique and the specific equipment required for autologous blood harvesting.

This clinical photograph illustrates a venipuncture procedure for blood collection from the antecubital fossa of a patient's arm. A blue reusable tourniquet is applied to the mid-humerus region to facilitate venous distension. A healthcare professional, wearing white sterile gloves, is performing the procedure using a winged infusion set (butterfly needle), indicated by the green plastic 'wings' held at the puncture site. The needle is connected via flexible tubing to a vacuum-sealed blood collection tube (vacutainer) with a red-stoppered cap. The setup demonstrates standard aseptic technique and equipment used for obtaining venous blood samples, which in this clinical context is being utilized for the subsequent preparation of Leukocyte-Platelet-Rich Fibrin (L-PRF) for surgical use.

Here is the complete, expanded master reference for every procedure on your checklist. Every step, every threshold, every pitfall.

COMPLETE INFECTIOUS WARD PROCEDURES - MASTER REFERENCE

1. PPD - Purified Protein Derivative (Mantoux Tuberculin Skin Test)

Mechanism

Intradermal injection triggers Type IV (delayed-type) hypersensitivity mediated by sensitized T lymphocytes. Detects M. tuberculosis infection - does NOT distinguish latent from active disease.

Indications

TB screening in close contacts of active TB cases
Healthcare workers (baseline and periodic)
HIV-positive patients and other immunocompromised patients
Pre-biologic therapy (anti-TNF agents: infliximab, adalimumab, etanercept)
Immigrants from high-prevalence countries
Residents/staff of congregate settings (prisons, shelters, nursing homes)
Suspected TB in any patient with compatible symptoms

Contraindications

Known active TB (no need to test)
Documented previous strongly positive reaction (severe ulceration/necrosis risk)
Prior severe reaction to tuberculin
Extensive burns or eczema at injection site

Technique - Step by Step

Draw 0.1 mL (5 tuberculin units) of PPD solution into a 1 mL tuberculin syringe with a 26-27G, 3/8-inch bevel-up needle
Select the volar (inner) forearm, 4 fingerbreadths below the antecubital fossa - avoid veins, scars, and hairy areas
Cleanse with alcohol and allow to dry
Stretch the skin taut and insert needle bevel-up at 5-15° angle, just under the skin (intradermally, NOT subcutaneously)
Inject slowly - a pale, raised bleb 6-10 mm should form. If no bleb forms, the injection was too deep (subcutaneous) - document and repeat at a different site
Do NOT massage the site after injection
Record the forearm used, lot number, and time

Reading (48-72 hours)

Mark the margins of induration (the palpable, raised, firm area) with a ballpoint pen using the "ballpoint pen roll" technique
Measure the transverse diameter (perpendicular to the long axis of the forearm) in millimeters
Record erythema separately but base interpretation on induration ONLY

Interpretation Thresholds

Induration	Population
≥ 5 mm	HIV-positive; recent close contact of active TB; fibrotic CXR changes consistent with old TB; organ transplant; patients on ≥15 mg/day prednisone; TNF inhibitor therapy
≥ 10 mm	Recent immigrants (<5 yrs) from high-prevalence countries; IVDU; residents/employees of congregate settings; mycobacteriology lab staff; children <4 years; medical risk factors (DM, silicosis, CKD, haematologic malignancies, weight loss >10%)
≥ 15 mm	All other persons with no risk factors

False Negatives (Anergy) - Remember "VMSAAHI"

Viral infections (measles, EBV, influenza, HIV)
Malnutrition
Sarcoidosis
Active overwhelming TB (paradoxical anergy in miliary TB)
Age extremes (<6 months, elderly)
Hodgkin lymphoma / haematologic malignancies
Immunosuppression (steroids, chemotherapy)

False Positives

BCG vaccination (especially if recent; reactions >15 mm unlikely to be BCG alone)
Nontuberculous mycobacteria (NTM) cross-reaction
Technical error (measuring erythema instead of induration)

Two-Step Testing

For baseline screening of adults who will be tested periodically (healthcare workers): perform a second PPD 1-3 weeks after the first negative. A positive on the second test = "boosted reaction" due to remote prior infection, NOT a new conversion. This establishes true baseline.

Tuberculin Conversion

A change from negative to positive (or increase of ≥10 mm) within 2 years = new infection. 3-4% will develop active TB in the first year after conversion.

PPD vs. IGRA

	PPD	IGRA (QuantiFERON, T-SPOT)
BCG cross-reaction	Yes	No
NTM cross-reaction	Yes	Minimal
Requires return visit	Yes (48-72h)	No (1 visit, blood test)
Reader variability	Yes	No
Preferred when	Low-cost setting, <5 yrs old	BCG-vaccinated, unreliable follow-up

2. تهیه لام خون محیطی - Peripheral Blood Smear Preparation

Indications in the Infectious Ward

Suspected malaria (most important - this is a medical emergency)
Sepsis evaluation (toxic granulation, left shift)
Infectious mononucleosis (atypical lymphocytes)
Haemolytic anaemia secondary to infection
Babesiosis, trypanosomiasis, relapsing fever (Borrelia)
Microfilaria (nocturnal periodicity - collect at midnight)
Baseline in any critically unwell febrile patient

Equipment

Clean glass slides (pre-degreased)
Fresh EDTA blood or fingerstick
Spreader slide or coverslip
Wright-Giemsa stain (preferred) or Field stain (for malaria)
Immersion oil, light microscope

Technique - Thin Smear (for identification)

Place a small drop (2-3 µL) of blood 1-2 cm from the frosted end of the slide
Place spreader slide at 30-45° angle, back it into the drop until blood spreads along the full width of the spreader
Push forward in one smooth, even, rapid stroke - do NOT pause or lift
The smear should show a feathered edge (cells in monolayer at the thin end)
Air-dry immediately - do NOT heat-fix or blow; this distorts morphology
Fix with methanol for 1-2 minutes, then stain with Giemsa (1:20 dilution for 45 min, or rapid Field stain)
Read under 10x (scan feathered edge), then 40x, then 100x oil immersion

Technique - Thick Smear (for sensitivity in malaria)

Place a large drop of blood in the centre of a slide and spread in a circular motion to a 1-2 cm circle
Air-dry for 30+ minutes (do NOT fix - the RBCs must lyse to expose parasites)
Stain with Giemsa (without methanol fixation)
Thick smears are ~20x more sensitive than thin smears for detecting parasites but cannot identify Plasmodium species

Standard Practice for Malaria

Make BOTH thick and thin smears simultaneously
If first smear is negative, repeat every 12-24 hours for 3 sets before ruling out malaria
Never rule out malaria on a single negative smear in a febrile returning traveller

Key Findings on Peripheral Smear in Infectious Disease

Finding	Significance
Ring forms within RBCs (multiple rings per cell, banana-shaped gametocytes)	P. falciparum - malaria, SEVERE
Enlarged RBCs with ring + Schüffner's dots	P. vivax or P. ovale
RBCs normal size, ring + "Maltese cross" (tetrad form)	Babesiosis
Trypomastigotes (C-shaped organisms in plasma)	African trypanosomiasis
Spiral organisms between RBCs	Relapsing fever (Borrelia)
Toxic granulation (dark granules in neutrophils)	Bacterial sepsis
Döhle bodies (blue cytoplasmic inclusions in neutrophils)	Severe bacterial infection, sepsis
Left shift (bands > 10%, metamyelocytes, myelocytes)	Bacterial infection, sepsis
Atypical lymphocytes (large, lobulated, monospot)	EBV mononucleosis, CMV, acute HIV
Neutropenia	Typhoid, viral infections, bone marrow suppression
Reactive thrombocytosis	Post-infection, asplenic patients
Thrombocytopenia	Malaria, dengue, HUS, sepsis, DIC
Schistocytes + thrombocytopenia	HUS, TTP (associated with STEC infection, HIV)

3. رنگ آمیزی گرم - Gram Staining

Purpose

Rapid (15-30 minute) classification of bacteria by cell wall structure, guiding empiric antibiotic choice before culture results.

Complete Step-by-Step Protocol

(from Jawetz Medical Microbiology)

Prepare smear: Spread specimen thinly on a clean glass slide; air-dry
Heat-fix: Pass the slide quickly through a flame 2-3 times, OR methanol-fix (more gentle, less distortion)
Crystal violet (primary stain): Flood slide, wait 60 seconds, rinse with tap water
Gram's iodine (mordant): Flood slide, wait 60 seconds - forms crystal violet-iodine complex inside all bacteria; rinse
Decolorizer (95% ethanol or acetone-alcohol): Apply for 5-10 seconds only - the most critical and error-prone step. Too long = over-decolorize Gram-positive cells (they appear Gram-negative); too short = Gram-negatives appear Gram-positive. Rinse immediately with water
Safranin (counterstain): Flood slide, wait 60 seconds; rinse; blot dry (do NOT rub)
Examine under 100x oil immersion

Results

Colour	Interpretation
Purple/violet	Gram-positive (thick peptidoglycan retains crystal violet-iodine complex)
Pink/red	Gram-negative (thin peptidoglycan, outer membrane loses complex on decolorization)

Key Organisms by Morphology

Morphology	Common Organisms	Clinical Context
Gram+ cocci in clusters	Staphylococcus aureus, CoNS	Abscess, bacteremia, endocarditis
Gram+ cocci in chains	Streptococcus spp., Enterococcus	Pharyngitis, pneumonia, UTI
Gram+ diplococci (lancet-shaped)	S. pneumoniae	Pneumonia, meningitis
Gram- diplococci (coffee bean, intracellular)	Neisseria meningitidis, N. gonorrhoeae	Meningitis, urethritis, joint infection
Gram- rods (straight)	E. coli, Klebsiella, Pseudomonas, Proteus	UTI, pneumonia, wound infection
Gram+ rods (large, box-car shaped)	Clostridium, Bacillus	Wound infection, gas gangrene
Gram+ rods (small, tumbling motility)	Listeria monocytogenes	Meningitis in neonates, elderly, immunocompromised
Branching Gram+ filaments	Actinomyces, Nocardia	Abscess, pulmonary infection
No organisms visible	Consider: anaerobes, mycobacteria, fungi, viruses - use special stains

Special Stains (when Gram stain is insufficient)

Stain	Used For	Result
Ziehl-Neelsen (AFB stain)	Mycobacteria, Nocardia	AFB = red/pink; background = blue
India ink	Cryptococcus neoformans in CSF	Clear halo (capsule) around organism
KOH preparation	Fungi	Clear fungal elements on dissolved background
Giemsa	Malaria, Chlamydia, Rickettsia	Varies
PAS	Fungi, Pneumocystis	Magenta cell walls

Common Gram Stain Errors

Error	Cause	Effect
Over-decolorized	Too long with acetone-alcohol	Gram+ appear pink (false Gram-)
Under-decolorized	Too little acetone-alcohol	Gram- appear purple (false Gram+)
Too thick smear	Overlapping cells	Poor resolution, missed organisms
Old culture	Aged bacteria lose Gram+ wall integrity	Gram-variable result

4. احتیاطات استاندارد و ایزولاسیون - Standard Precautions and Isolation

Standard Precautions (apply to EVERY patient, ALWAYS)

These are the minimum baseline for all patient care:

Hand hygiene - the single most effective infection control measure
- Alcohol-based hand rub (ABHR): before/after patient contact, after touching patient surroundings, before clean/aseptic procedures, after body fluid exposure
- Soap and water: when hands are visibly soiled, after C. difficile exposure (alcohol does NOT kill spores), after norovirus exposure
- Minimum 20 seconds for soap, 15-25 seconds for ABHR (rub until dry)
Gloves: for contact with blood, body fluids, mucous membranes, non-intact skin
Mask + eye protection/face shield: when splash/spray of blood or body fluids is possible
Gown/apron: when clothing/skin may become contaminated
Safe sharps handling: never recap by two-handed technique; use safety devices; sharps container at point of use, replaced at 2/3 full
Respiratory hygiene/cough etiquette: mask on coughing patients, tissues available, hand hygiene
Safe injection practices: one needle, one syringe, one patient, one time
Aseptic technique: sterile field, sterile equipment for invasive procedures
Environmental cleaning: routine cleaning of surfaces; terminal clean on discharge

Skin Antisepsis for Procedures

Immunisation and routine venipuncture: 70% isopropyl alcohol (allow to air-dry)
Blood cultures, incision, IV catheter insertion: 2% chlorhexidine gluconate in 70% isopropyl alcohol (allow to dry 30 seconds) - Red Book (AAP)
Neonates <2 months and mucous membranes: use povidone-iodine (chlorhexidine is NOT approved for <2 months)

Transmission-Based Precautions

Type	Transmission Route	PPE Required	Room	Duration	Pathogens
Contact	Direct skin-to-skin or indirect via fomites	Gloves + gown (on room entry)	Single room or cohort	Until resolved	MRSA, VRE, C. difficile, scabies, impetigo, Shigella, norovirus, RSV
Droplet	Large droplets (>5 µm) - travel <1 metre	Surgical mask (on room entry), gloves	Single room; door may stay open	Until resolved (or for influenza: 5 days after symptom onset, 10 days if immunocompromised)	Influenza, meningococcal disease, pertussis, mumps, rubella, Haemophilus influenzae meningitis, SARS-CoV-2 (routine)
Airborne	Small droplet nuclei (<5 µm) - remain suspended in air, travel >1 metre	N95 respirator (fit-tested, seal-checked); gown + gloves	Negative-pressure room (≥12 air changes/hour), door kept CLOSED	TB: until 3 negative AFB smears on 3 consecutive days; measles/varicella: until lesions crusted	TB, measles, varicella/disseminated zoster, SARS-CoV-2 (aerosol-generating procedures)
Protective (Reverse)	Protect immunocompromised patient FROM environment	Mask on visitors + staff, gown + gloves	Positive-pressure room, HEPA filtration, avoid fresh flowers/plants	Duration of immunosuppression	Neutropenic patients (ANC <500), BMT recipients, severe combined immunodeficiency

Donning (Putting On) Order

Gown → Mask/respirator → Eye protection/face shield → Gloves

Doffing (Removing) Order - MOST CRITICAL (self-contamination risk)

Gloves → Eye protection → Gown → Mask/respirator → Hand hygiene after EACH step

Clostridium difficile - Special Precautions

Contact precautions + soap and water hand hygiene (ABHR does NOT kill spores)
Dedicated equipment (stethoscope, BP cuff, thermometer)
Environment: clean with 10% bleach or sporicidal agent
Maintain precautions for at least 48 hours after diarrhoea resolves

5. گرفتن نمونه کشت خون - Blood Culture Collection

When to Order

Fever ≥38.3°C or hypothermia <36°C in a hospitalised patient
Suspected bacteremia or fungemia
Before starting empiric antibiotics whenever possible
Suspected endocarditis, septic arthritis, meningitis, osteomyelitis
New onset of rigors/chills
Unexplained hypotension or organ dysfunction

Equipment

2 sets of bottles (each set = 1 aerobic + 1 anaerobic)
Sterile gloves, tourniquet
2% chlorhexidine-alcohol swabs (or povidone-iodine for neonates)
20-22G needle or butterfly (winged infusion set)
20-50 mL syringe or vacutainer system

Technique - Step by Step

Two separate sites: Draw each set from a different venipuncture site (different arm, or arm + other site) - this is mandatory for interpretation of contaminants
Antiseptic prep of bottles: Wipe the bottle rubber tops with 70% isopropyl alcohol; allow to dry
Skin antisepsis: Apply 2% chlorhexidine-alcohol in a concentric circle from centre outward; wait 30 seconds to dry completely; do NOT touch the site again
Draw blood:
- Adults: 8-10 mL per bottle (10 mL optimum)
- Paediatrics: 1-3 mL per bottle (or paediatric bottles with 1-5 mL)
- Total adult draw: typically 20 mL (10 mL × 2 bottles per set)
Inoculation order:
- With a syringe: aerobic bottle first (to prevent introducing air into anaerobic)
- With a butterfly/winged set: anaerobic bottle first (the tubing contains air - fill aerobic last after air is flushed)
Gently invert bottles 8-10 times to mix blood with broth (prevents clotting)
Label with: patient ID, date, time, collection site (e.g., "right antecubital fossa"), bottle number
Transport to microbiology lab within 2 hours at room temperature (NOT refrigerated)

Volume Effect on Yield

Each additional 1 mL of blood increases recovery by ~3%. This is why volume is the single most important variable:

5 mL/bottle → ~50-60% sensitivity for bacteremia
10 mL/bottle → ~80-90% sensitivity
2 sets (20-30 mL total) → 80-90% detection
3 sets → ~96% detection

Timing

Draw before antibiotics whenever possible - even one dose reduces yield by 30-40%
In suspected endocarditis: draw 3 sets over 30-60 minutes before starting antibiotics
In septic shock: draw 2 sets simultaneously, do NOT delay antibiotics beyond 1 hour for culture collection
In suspected fungemia: hold bottles for up to 5 weeks (fungi grow slowly; standard incubation is 5 days)

Interpreting Results

Organism	1/2 bottles positive	2/2 sets positive
S. aureus	Likely true (always treat)	Definite bacteremia
E. coli, Klebsiella, Pseudomonas	Likely true	Definite bacteremia
CoNS (S. epidermidis)	Likely contaminant	Consider true if indwelling catheter
Bacillus, Corynebacterium, Propionibacterium	Almost always contaminant	Rarely true pathogen
Candida spp.	Always significant - fungemia	Mandates antifungal therapy
S. pneumoniae, Listeria	Always significant	Always treat

Common Contaminants ("SPACE")

Staphylococcus epidermidis (CoNS)
Propionibacterium acnes
Aerococcus / Alpha-haemolytic streptococci (viridans group)
Corynebacterium (diphtheroids)
Enterococcus (when single set only)

6. گرفتن نمونه کشت حلق - Throat Culture

Indications

Suspected Group A Streptococcus (GAS) pharyngitis (most common)
Suspected diphtheria (grey membrane, bull neck, toxicity)
Suspected gonococcal pharyngitis (N. gonorrhoeae)
Peritonsillar abscess (pus swab)
Suspected Candida pharyngitis
Epidemiological screening for carriers (MRSA nares + throat)
Contact investigation for diphtheria or meningococcal carriage

Equipment

Sterile Dacron or rayon swab (NOT cotton - inhibits some organisms)
Tongue depressor
Light source
Transport medium (Amies or Stuart's, or specific media for gonococci: Thayer-Martin)
Rapid antigen detection test (RADT) kit if available

Technique - Step by Step

Explain the procedure, reassure the patient
Position patient with mouth wide open and head tilted back; use good lighting
Use tongue depressor to depress the tongue firmly - expose the posterior pharynx and tonsils
Ask patient to say "Aaah" - this elevates the uvula and exposes the posterior wall
Swab in this order: tonsillar crypts (right and left) → any visible exudate or membrane → posterior pharyngeal wall
Apply firm, rotating pressure - vigorous sampling improves yield
AVOID: tongue, teeth, lips, buccal mucosa, uvula, saliva - all are contaminants
Place swab in transport medium immediately
If diphtheria is suspected: send a second swab and specifically alert the laboratory ("Please culture for Corynebacterium diphtheriae on Loeffler's/tellurite agar")

Rapid Antigen Detection Test (RADT) for GAS

Sensitivity: 70-90%; Specificity: 95-99%
Positive RADT: treat without culture
Negative RADT in adults: may accept (low GAS prevalence in adults means negative predictive value is high)
Negative RADT in children: confirm with culture (guidelines recommend backup culture in children due to higher GAS rates and rheumatic fever risk)
Read result at exactly the time specified (usually 5 minutes)

Media for Throat Culture

Organism	Media
GAS (S. pyogenes)	Blood agar (5% sheep blood) - beta haemolysis at 24-48h
Diphtheria	Loeffler's serum slope + Tellurite (CTBA) agar
N. gonorrhoeae	Modified Thayer-Martin (chocolate agar with antibiotics) - transport in CO₂
Candida	Sabouraud dextrose agar

Interpretation

GAS on culture: treat with amoxicillin (10 days) or penicillin V. Failure to treat → risk of acute rheumatic fever and post-streptococcal glomerulonephritis
Do NOT swab in suspected epiglottitis (hot potato voice, drooling, stridor, tripod position) - risk of laryngospasm. Go directly to airway management and ENT/anaesthesia

Centor/McIsaac Criteria (for GAS probability)

Score 1 point each for: tonsillar exudates, tender anterior cervical lymphadenopathy, absence of cough, fever ≥38°C. Add 1 point if age <15 yrs; subtract 1 if age ≥45 yrs.

Score ≤1: No testing, no antibiotics
Score 2-3: RADT; treat only if positive
Score ≥4: Treat empirically (or test and treat)

7. نمونه از زخم پوستی - Skin and Wound Sampling

Indications

Cellulitis with purulent component (abscess, furuncle, carbuncle)
Infected surgical or traumatic wound
Diabetic foot ulcer
Pressure ulcer with signs of infection (purulence, odour, surrounding cellulitis)
Suspected necrotizing fasciitis
Cutaneous TB, leishmaniasis, atypical mycobacteria
Infected bite wounds (human, animal)
Ecthyma, impetigo not responding to empiric therapy

Technique by Wound Type

1. Abscess / Closed Collection (PREFERRED: aspiration)

Clean skin with chlorhexidine-alcohol
Insert a 18-20G needle and aspirate pus
Send aspirate for Gram stain, aerobic + anaerobic culture
Send additional samples for AFB if mycobacterium suspected
Aspiration before incision gives the cleanest, most diagnostic specimen

2. Open Wound / Ulcer - Levine Technique (gold standard)

Irrigate wound with sterile saline first to remove surface bacteria (surface swabs are unreliable and show colonisers, not pathogens)
Press a Dacron swab firmly over a 1 cm² area of viable wound bed tissue
Rotate swab for 5 seconds with enough pressure to express fluid from the wound tissue
Avoid necrotic slough, eschar, or pus pockets (these give misleading results)

3. Tissue Biopsy (best for deep infections)

Obtain under sterile conditions (punch biopsy 4-6 mm, or surgical excision)
Place in sterile container with a small amount of sterile saline (NOT formalin for culture)
Send half to microbiology (C&S, AFB, fungal) and half to histopathology
Best for: necrotizing fasciitis, osteomyelitis, leishmaniasis, cutaneous TB, actinomycosis

4. Vesicle / Blister

Unroof the blister with a needle
Swab the base (not the blister fluid - virus is in the cells at the base)
Send for: Tzanck smear (HSV shows multinucleated giant cells), viral PCR or DFA for HSV/VZV
For intact vesicles: aspirate fluid with a fine needle

5. Sinus Tract

Do NOT swab the opening - this reflects surface colonisers only
Probe the tract and sample the deepest accessible tissue
Best approach: aspirate from the deepest part or biopsy

Special Stains / Tests for Skin Specimens

Suspected Organism	Test
Mycobacterium (TB, NTM)	AFB smear + culture on Lowenstein-Jensen media (4-8 weeks); PCR
Leishmania	Giemsa smear (look for amastigotes in macrophages); NNN media culture; PCR
Fungi (dermatophytes)	KOH prep; Sabouraud agar
HSV/VZV	Tzanck smear; PCR (most sensitive)
Actinomyces	Gram stain (Gram+ branching filaments); anaerobic culture
Nocardia	Modified AFB stain (weakly acid-fast); aerobic culture

Key Pitfalls

Always sample BEFORE cleaning the wound with antibacterials
Superficial swabs of chronic wounds represent colonisation only - they should NOT drive antibiotic prescribing without clinical correlation
Necrotizing fasciitis: send peroperative tissue from the advancing edge - do not wait for microbiological confirmation before surgery

8. لومبار پونکسیون - Lumbar Puncture

Indications

Suspected meningitis or encephalitis (most urgent)
Suspected subarachnoid haemorrhage with negative CT
Suspected CNS TB, cryptococcal meningitis, carcinomatous meningitis
Neurosyphilis, Lyme neuroborreliosis
Measuring intracranial pressure (e.g., idiopathic intracranial hypertension)
Intrathecal drug delivery (antibiotics, chemotherapy)
Myelography/cisternography

When to Do CT FIRST (before LP)

Do NOT perform LP if any of the following are present - get CT scan first: (from Pfenninger & Fowler's, Straus et al. JAMA 2006)

Papilledema (note: absent in up to 15% adults and 50% children with early raised ICP)
Altered level of consciousness
Focal neurological signs (focal deficit, gaze palsy, arm/leg drift, facial palsy)
Seizure within 1 week
Age ≥60 years with new neurological symptoms
Immunocompromised state
History of CNS disease (mass lesion, stroke, focal infection)

BUT: Do NOT delay antibiotics for CT or LP in suspected bacterial meningitis - give ceftriaxone + dexamethasone empirically, THEN do CT, THEN LP.

CT findings that contraindicate LP:

Midline shift
Loss of suprachiasmatic or basilar cisterns
Posterior fossa mass or cistern obliteration

Absolute Contraindications

Local skin/soft tissue infection at puncture site
Uncorrected coagulopathy (INR >1.4) or severe thrombocytopenia (platelets <20,000; relative if dropping rapidly)

Relative Contraindications

Unstable patient (hypotension, shock, status asthmaticus) - stabilise first
Anticoagulation (warfarin, heparin, NOACs) - consider risk/benefit; use smallest gauge needle if proceeding
Spinal stenosis, prior lumbar surgery (may need fluoroscopic guidance)

Equipment

Sterile drape and gloves, chlorhexidine prep
20-22G spinal needle with stylet (22G preferred - lower post-LP headache rate)
Manometer and 3-way stopcock
4 sterile collection tubes (numbered 1-4)
Local anaesthetic (1% or 2% lidocaine, 25G needle)

Technique - Step by Step

(from Neuroanatomy through Clinical Cases 3e)

Positioning:

Lateral decubitus (lying on side): preferred for pressure measurement. Patient lies in the fetal position - hips, knees, and neck maximally flexed to open posterior intervertebral spaces. An assistant can help the patient maintain flexion.
Seated position: sit patient upright, leaning forward with arms crossed on a pillow. Good for obese patients. Pressure measurement less reliable (hydrostatic column of CSF adds to pressure).

Landmark:

Draw an imaginary line connecting the tops of the posterior superior iliac crests - this crosses the spine at the L4 spinous process (or L4-L5 interspace)
Insert at L3-L4 or L4-L5 (both are safe - the conus medullaris ends at L1-L2)
Palpate the spinous processes and identify the midline and interspinous space

Procedure:

Prep skin with chlorhexidine in concentric circles; allow to dry; apply sterile drape
Infiltrate local anaesthetic into skin and subcutaneous tissues at the chosen space
Insert spinal needle bevel-UP (bevel parallel to dural fibres - reduces post-LP headache) in the midline, angled slightly cranially (toward umbilicus)
Advance slowly - feel resistance as you pass through skin, subcutaneous fat, supraspinous ligament, interspinous ligament, ligamentum flavum, then a distinct "pop" as you enter the epidural and then subarachnoid space
Remove the stylet and check for CSF flow
Measure opening pressure with manometer in cm H₂O (patient must be relaxed, legs extended slightly for accuracy)
- Normal: <20 cm H₂O (or <25 cm H₂O in some references)
- Elevated in: bacterial meningitis, cryptococcal meningitis, SAH, IIH, cerebral venous sinus thrombosis
Collect CSF into 4 numbered tubes, 1-2 mL each, in sequential order:
- Tube 1: Cell count and differential (may have RBCs from traumatic tap at start)
- Tube 2: Biochemistry (protein, glucose - always send paired serum glucose simultaneously)
- Tube 3: Microbiology (Gram stain, C&S, AFB, India ink, cryptococcal antigen, viral PCR)
- Tube 4: Cell count again (compare to Tube 1 to distinguish traumatic tap from true haemorrhage)
Replace stylet before withdrawing needle (reduces post-LP headache)
Apply pressure dressing; patient may lie flat for 1 hour

CSF Interpretation Table

Parameter	Normal	Bacterial Meningitis	Viral Meningitis	TB/Fungal Meningitis
Appearance	Clear, colourless	Turbid/cloudy, may be purulent	Clear	Clear to slightly turbid/xanthochromic
Opening pressure	<20 cm H₂O	Markedly elevated (>30 cm H₂O)	Normal or mildly elevated	Elevated
WBC (cells/µL)	0-5 (lymphocytes)	>1000, often >10,000	10-1000	100-500
Cell type	Lymphocytes	Neutrophils (>80%)	Lymphocytes	Lymphocytes
Protein (mg/dL)	15-45	Very high: >100-500	Normal or slightly raised (45-100)	High: 100-500
Glucose (mg/dL)	50-80 (or >60% of serum)	Very low: <40 (often <20)	Normal (>60% serum)	Low: <45
CSF:serum glucose ratio	>0.6	<0.4	>0.6	<0.5
Gram stain	Negative	Positive in 60-80%	Negative	Negative (AFB positive in <40%)
Organisms	None	Bacteria	None	India ink: Crypto; AFB: TB
Other tests		Bacterial antigen panel; PCR	Viral PCR (HSV, enterovirus)	Cryptococcal Ag; AFB culture; ADA level

Traumatic Tap vs. True Subarachnoid Haemorrhage

Feature	Traumatic Tap	SAH
RBCs in CSF	Present	Present
RBC count across tubes 1→4	Decreasing	Unchanged
Xanthochromia (after centrifugation)	Absent (if processed immediately)	Present (develops 2-4 hours after bleed)
Clotting in tubes	May occur	Rarely clots

Complications

Post-LP headache (1-70%): positional, bilateral, frontal-occipital, worsens upright, relieved supine. Usually resolves in days. Treatment: bed rest, oral hydration, caffeine, NSAIDs. Refractory: epidural blood patch (10-20 mL autologous blood) - most effective treatment, >90% success.
Herniation (rare if contraindications are respected)
Local back pain (common, transient)
Bleeding (epidural haematoma - rare, most relevant in coagulopathic patients)
Infection (bacterial meningitis, epidural abscess - rare with strict asepsis)
Nerve root irritation / radicular pain (needle touches a nerve root - withdraw and redirect)

9. تفسیر آزمایشات - Interpretation of Lab Tests

CBC with Differential - Infectious Ward Interpretation

WBC Pattern	Significance
Neutrophilia (>7,500/µL) with left shift	Bacterial infection, stress, steroid use, early sepsis
Band forms > 10%	Bacterial infection, early sepsis ("left shift")
Neutropenia (<1,500/µL)	Viral infections (typhoid, dengue, influenza), drugs, sepsis-induced bone marrow suppression
Lymphocytosis	Viral infections (EBV, CMV, acute HIV, pertussis), TB
Atypical lymphocytes > 10%	EBV, CMV, acute HIV, toxoplasmosis, hepatitis
Monocytosis	TB, brucellosis, typhoid, fungal infections, EBV
Eosinophilia	Parasitic infections (helminths esp.), fungal infections, drug reaction
Basophilia	Rare in infection; consider haematologic malignancy
Thrombocytopenia	Dengue (hallmark), malaria, sepsis-induced DIC, HUS, typhoid, HIV
Thrombocytosis (reactive)	Post-infectious, post-splenectomy

Key Infection Biomarkers

Biomarker	Reference Range	Interpretation
CRP	<5 mg/L	Rises within 6 hours, peaks at 48h. Rises with any inflammation (bacterial, viral, tissue damage). Not specific. Serial values more useful than single value.
ESR	<20 mm/hr (men), <30 mm/hr (women)	Slow to rise (24-48h), slow to normalise. Useful for chronic infections (TB, osteomyelitis, infective endocarditis) and monitoring treatment response.
Procalcitonin (PCT)	<0.1 ng/mL	PCT >0.5 ng/mL = suggestive of bacterial infection. PCT <0.1 ng/mL = bacterial infection less likely. PCT-guided protocols can safely reduce antibiotic duration in respiratory infections and sepsis. Caution: low PCT does NOT exclude severe bacterial infection - Washington Manual. Elevated in: bacterial sepsis, invasive fungal infection, severe burns/trauma. NOT elevated in: viral infections, localised infections (abscess without bacteremia), autoimmune disease.
Lactate	<2 mmol/L	>2 mmol/L = tissue hypoperfusion. Lactate ≥4 = septic shock. Serial lactate guides resuscitation (normalisation target per Surviving Sepsis Guidelines).
Ferritin	Variable	Markedly elevated (>10,000 µg/L) in: haemophagocytic lymphohistiocytosis (HLH), adult-onset Still's disease, severe sepsis, cytokine storm.

Serology Interpretation

Pattern	Meaning
IgM positive, IgG negative	Acute/primary infection (within 1-2 weeks)
IgM positive, IgG positive	Recent infection (1-4 weeks, still in acute phase)
IgM negative, IgG positive	Past infection or vaccination (immunity)
Both negative	Not infected, no immunity
4-fold rise in IgG titre (paired acute + convalescent, 2-4 weeks apart)	Confirms recent infection even if IgM is equivocal

HIV Testing

4th generation Ag/Ab combo test: detects both HIV p24 antigen AND antibodies → shortens window period to ~18 days from exposure. Reactive result requires confirmatory testing (HIV-1/HIV-2 differentiation assay + HIV RNA viral load).
Window period: Ag/Ab test = 18-45 days. If exposure is <18 days ago, test is unreliable - retest at 45 days and 90 days.
Viral load: undetectable (<50 copies/mL on ART) = treatment success + prevents transmission. Detectable on ART = assess adherence, resistance testing.
CD4 count: <200/µL = AIDS-defining; <50/µL = risk for CMV retinitis, MAC, Cryptococcus, PCP.

Dengue Serology (NS1 + IgM/IgG)

Day of Illness	NS1 Ag	IgM	IgG	Interpretation
Days 1-5	+	-	-	Early primary dengue
Days 5-9	±	+	-	Primary dengue
Days 5-9	±	+	+	Secondary dengue (worse prognosis, risk of severe dengue)
Day >10	-	+	+	Late primary or secondary dengue

Urinalysis in Infection

Pyuria (>5 WBC/hpf) + bacteriuria + symptoms = UTI
Sterile pyuria (WBC without bacteria): TB, partly-treated UTI, renal TB, Chlamydia urethritis
Nitrites: positive = Gram-negative bacteria (Enterobacteriaceae); absence does not rule out UTI (Enterococcus, S. saprophyticus, Pseudomonas are nitrite-negative)
Leucocyte esterase: proxy for WBCs; positive + nitrites = ~85% sensitivity for UTI

Renal Function - Antibiotic Dose Adjustment

Drug	Adjustment Required in Renal Impairment
Aminoglycosides (gentamicin, amikacin)	Reduce dose OR extend interval; monitor trough levels; target trough <1 mg/L (gentamicin); nephrotoxic + ototoxic
Vancomycin	Reduce frequency (AUC/MIC guided dosing); target AUC 400-600 mg·h/L; monitor troughs or AUC
Acyclovir / Valacyclovir	Reduce dose; risk of crystalline nephropathy and encephalopathy
Fluconazole	Reduce dose by 50% if eGFR <50; IV formulation contains cyclodextrin - avoid if eGFR <50
Piperacillin-tazobactam	Reduce dose/extend interval if eGFR <40
Carbapenems	Dose reduction needed (all)
Colistin	Careful dose adjustment; highly nephrotoxic

Sources used:

Robbins & Kumar Basic Pathology - PPD/tuberculin test
Robbins, Cotran & Kumar Pathologic Basis of Disease - TB, PPD interpretation
Jawetz, Melnick & Adelberg's Medical Microbiology 28e - Gram staining
Neuroanatomy through Clinical Cases 3e - Lumbar puncture technique
Pfenninger & Fowler's Procedures for Primary Care - LP contraindications
Red Book 2021 (AAP Committee on Infectious Diseases) - Standard precautions, blood culture antisepsis
The Washington Manual of Medical Therapeutics - Procalcitonin, sepsis biomarkers
Fishman's Pulmonary Diseases - Procalcitonin in respiratory infection

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