---

HEMATOLOGY - COMPREHENSIVE ANSWERS

---

Q1. Hemorrhagic Disorders & Hemophilia

Definition of Hemorrhagic Disorders

Classification of Hemorrhagic Disorders

1. Vascular disorders - Hereditary hemorrhagic telangiectasia, scurvy, Henoch-Schonlein purpura
2. Platelet disorders - Thrombocytopenia, thrombocytopathy (qualitative defects)
3. Coagulation factor deficiencies - Hemophilia A & B, von Willebrand disease, DIC, liver disease

---

HEMOPHILIA

• Genetics: X-linked recessive - carried on the X chromosome, almost exclusively affects males (XY)
• Inheritance: Female carriers (X^H X) transmit to 50% of sons (affected) and 50% of daughters (carriers)
• Molecular basis: Deletions, inversions, point mutations in the F8 or F9 gene on the X chromosome
• Approximately one-third of cases arise from new mutations (no family history)
• Rarely, females can be affected via Turner syndrome (45,X), extreme lyonization, or if homozygous

• The extrinsic pathway (tissue factor/factor VIIa) can generate thrombin initially, producing a primary platelet plug normally
• However, sustained thrombin generation via the intrinsic amplification loop is severely impaired
• Clots form slowly, break down prematurely, and fail to achieve adequate hemostasis

• Hemarthroses (hallmark): blood in joint spaces - knees most commonly, followed by elbows, ankles, hips, shoulders
• Chronic hemarthrosis leads to: synovial inflammation, cartilage destruction, joint fibrosis, epiphyseal overgrowth, limb length discrepancy, generalized osteopenia
• Intramuscular hematomas: particularly iliopsoas (can compress femoral nerve)
• Pseudotumors: encapsulated blood cysts from repeated intramuscular bleeding
• Squaring of the patella and condyles on imaging (chronic hemophilic arthropathy)

• Spontaneous hemarthrosis - painful, warm, swollen joint with restricted range of motion
• Deep soft tissue bleeding (vs. petechiae in platelet disorders)
• Prolonged bleeding after dental extraction, surgery, or circumcision
• Retroperitoneal and intracranial hemorrhage in severe cases
• Hematuria
• Primary platelet plug is normal - superficial cuts may stop bleeding initially

• The aPTT tests the intrinsic and common pathways; PT tests the extrinsic and common pathway
• In hemophilia, only the intrinsic pathway is deficient, so PT is normal and aPTT is prolonged
• Mixing study: patient plasma + normal plasma normalizes aPTT (factor deficiency, not inhibitor)
• Factor-specific assay confirms diagnosis and quantifies severity
• von Willebrand factor antigen and activity should also be measured to exclude vWD (where factor VIII may be low)

---

Q2. Laboratory Diagnosis in a Case of Bleeding Gums

Causes to Consider

1. Local/dental: Gingivitis, periodontitis, calculus
2. Platelet disorders: Thrombocytopenia (ITP, aplastic anemia, leukemia), thrombocytopathy (aspirin, uremia)
3. Coagulation defects: Liver disease, hemophilia, DIC
4. Vascular disorders: Scurvy (vitamin C deficiency), hereditary hemorrhagic telangiectasia
5. Drugs: Anticoagulants (warfarin, heparin), antiplatelets

Laboratory Evaluation - Step-by-Step

• vWF antigen (quantitative)
• vWF ristocetin cofactor activity (functional)
• Factor VIII coagulant activity
• vWF multimer analysis

---

Q3. Thrombocytopenia - Classification & Primary ITP

Classification of Thrombocytopenia

• Aplastic anemia (bone marrow failure)
• Leukemia / myelodysplastic syndrome (marrow infiltration)
• Megaloblastic anemia (B12/folate deficiency)
• Chemotherapy, radiation
• Viral infections (HIV, CMV, EBV, hepatitis)
• Inherited: Fanconi anemia, amegakaryocytic thrombocytopenia

• Immune-mediated:
  • Primary immune thrombocytopenia (ITP)
  • Secondary ITP (SLE, HIV, HCV, medications)
  • Drug-induced thrombocytopenia (DITP: heparin/HIT, quinine)
  • Post-transfusion purpura
• Non-immune:
  • TTP (thrombotic thrombocytopenic purpura)
  • HUS (hemolytic uremic syndrome)
  • DIC
  • HELLP syndrome

• Hypersplenism (portal hypertension, storage diseases)

• Massive transfusion

---

PRIMARY IMMUNE THROMBOCYTOPENIA (ITP)

1. Autoantibody production: Autoreactive B cells produce IgG autoantibodies (predominantly IgG1 and IgG3) directed against platelet surface glycoproteins, mainly GPIIb/IIIa (fibrinogen receptor, integrin αIIbβ3) and GPIb/IX (vWF receptor)
2. Splenic destruction: Antibody-coated platelets are recognized by Fc receptors on splenic macrophages and destroyed by phagocytosis (extravascular destruction) - the spleen is the primary site
3. Impaired megakaryopoiesis: Anti-GPIIb/IIIa antibodies can bind to megakaryocytes, impairing platelet production and causing premature fragmentation - hence thrombopoietin levels may be lower than expected
4. T-cell dysregulation: Loss of regulatory T cells (Treg), skewing toward Th1/Th17 responses, cytotoxic T-cell-mediated platelet destruction
5. Liver: Secondary site of platelet destruction (Kupffer cells)

• Acute ITP (children): Abrupt onset after viral illness (2-3 weeks prior), predominantly ages 2-6 years, platelet count often <20,000/µL, >90% spontaneous remission within weeks-months
• Chronic ITP (adults): Insidious onset, female predominance (3:1), platelet count 30,000-100,000/µL, mucocutaneous bleeding (petechiae, purpura, ecchymoses, gum bleeding, menorrhagia)
• Signs: petechiae (especially in dependent areas), purpura, mucosal bleeding; splenomegaly is usually absent (distinguishes from secondary causes)
• Life-threatening: intracranial hemorrhage at platelet counts <10,000/µL

---

Q4. Laboratory Evaluation of Hemoglobinopathies

Laboratory Approach

• Microcytic hypochromic anemia: thalassemia, HbE, HbC trait
• Normocytic or macrocytic anemia with evidence of hemolysis: sickle cell disease
• Mentzer index (MCV/RBC): <13 suggests thalassemia; >13 suggests iron deficiency
• Target cells (codocytes): prominent in HbC disease, thalassemia, HbSC
• Sickle cells: HbSS, HbSC
• Nucleated RBCs, polychromasia: hemolysis or extramedullary hematopoiesis

• Sickle cell disease: sickle cells, target cells, Howell-Jolly bodies (asplenia), polychromasia
• Thalassemia major: hypochromic microcytic, target cells, nucleated RBCs, poikilocytosis, basophilic stippling
• HbC: abundant target cells, intracellular HbC crystals ("bar of gold")
• HbH disease (alpha-thalassemia): inclusion bodies with brilliant cresyl blue stain

• Performed on cellulose acetate (alkaline pH 8.4) and citrate agar (acid pH 6.0)
• At alkaline pH: HbA (fastest), then HbF, HbS, HbC (slowest)
• HbS and HbD co-migrate at alkaline pH but separate at acid pH (important for HbS confirmation)
• Detects: HbS, HbC, HbE, HbD, HbH, elevated HbF, elevated HbA2

• Ion-exchange chromatography separates hemoglobin variants by retention time
• Quantifies HbA, HbA2, HbF, HbS, HbC, and other variants
• HbA2 >3.5% + microcytosis = beta-thalassemia trait
• HbF elevated in HPFH, sickle cell disease, beta-thalassemia
• Can detect variants missed by electrophoresis

• PCR-based genotyping for known mutations (e.g., HbS: Glu6Val, beta-zero/beta-plus mutations)
• Gap-PCR for alpha-globin deletions (--SEA, -alpha3.7, -alpha4.2)
• Multiplex MLPA or NGS for comprehensive hemoglobin gene panel
• Prenatal diagnosis: chorionic villus sampling (CVS) at 10-12 weeks

---

Q5. Hemolytic Anemias - Classification & Immune Hemolytic Anemia

Definition

Classification

1. Membrane defects: Hereditary spherocytosis, hereditary elliptocytosis
2. Enzyme defects: G6PD deficiency, pyruvate kinase deficiency
3. Hemoglobinopathies: Sickle cell disease, thalassemia, HbC

1. Immune: Autoimmune hemolytic anemia (AIHA), alloimmune (transfusion reactions, HDN)
2. Microangiopathic: TTP, HUS, DIC, prosthetic heart valves
3. Infectious: Malaria (falciparum), clostridial sepsis, Bartonella
4. Chemical/toxic: Dapsone, lead poisoning
5. Hypersplenism

---

IMMUNE HEMOLYTIC ANEMIA (IHA / AIHA)

1. Drug adsorption (hapten) mechanism: Drug (e.g., penicillin) binds firmly to RBC membrane; antibody to drug-RBC complex causes hemolysis
2. Immune complex (innocent bystander): Drug-antibody complexes adsorb onto RBCs and activate complement (e.g., quinine)
3. Autoantibody induction: Drug induces true autoantibodies to RBC (e.g., methyldopa, fludarabine)

• ANA, anti-dsDNA: exclude SLE
• SPEP/immunofixation: lymphoproliferative disease
• HIV, EBV, Mycoplasma serology: secondary causes
• Drug history review

• Osmotic fragility (hereditary spherocytosis if AIHA excluded by negative DAT)
• G6PD assay (after acute hemolysis resolves, as reticulocytes have higher G6PD)
• Hb electrophoresis / HPLC (hemoglobinopathies)
• ADAMTS13 level (TTP if schistocytes present)
• Flow cytometry for CD55/CD59 (PNH - complement-mediated intravascular hemolysis)

---

Q6. Erythroblastosis Fetalis (Hemolytic Disease of the Newborn - HDN)

Definition

Etiology and Pathogenesis

1. Sensitization: An Rh-negative (Rh D-negative) mother carries an Rh-positive fetus. At delivery (or during abortions/invasive procedures), fetal Rh-positive RBCs enter the maternal circulation (fetomaternal hemorrhage), stimulating maternal IgM (primary response, does not cross placenta)
2. Re-exposure: In a subsequent Rh-positive pregnancy, the mother rapidly produces IgG anti-D antibodies (anamnestic/secondary response)
3. Transplacental passage: IgG (unlike IgM) freely crosses the placenta via FcRn receptors and binds to fetal RBCs
4. Fetal hemolysis: Antibody-coated fetal RBCs are destroyed by macrophages (splenic and hepatic), causing hemolytic anemia
5. Compensation: Compensatory erythropoiesis - first in bone marrow, then extramedullary (liver, spleen causing hepatosplenomegaly), releasing immature nucleated RBCs (erythroblasts) - giving the disease its name

Consequences

• Fetal anemia: Compensated by extramedullary hematopoiesis
• Hydrops fetalis: Severe anemia causes high-output cardiac failure, generalized edema, ascites, pleural effusions, hypoproteinemia
• Hyperbilirubinemia after birth: Placenta removes bilirubin in utero; after delivery, the neonate's immature liver cannot conjugate the bilirubin load from ongoing hemolysis
• Kernicterus: Unconjugated (lipophilic) bilirubin crosses the blood-brain barrier, depositing in basal ganglia, hippocampus, and other areas, causing permanent neurological damage, choreoathetosis, sensorineural deafness, and intellectual disability

Laboratory Diagnosis

Spectrophotometric Analysis of Amniotic Fluid (Liley Test)

• Zone I: mild/no disease
• Zone II: moderate disease - requires close monitoring
• Zone III: severe disease - immediate delivery or intrauterine transfusion

Treatment

• Phototherapy (converts bilirubin to water-soluble isomers)
• Exchange transfusion (removes antibody-coated RBCs and reduces bilirubin)
• Intrauterine transfusion for severe fetal anemia
• Prevention: Anti-D immunoglobulin (Rh-Ig, RhoGAM) given to Rh-negative mothers at 28-30 weeks gestation and within 72 hours of delivery of an Rh-positive baby - this passive anti-D clears fetal RBCs before maternal sensitization can occur

---

Q7. Polycythemia - Classification and Discussion

Definition

Classification

POLYCYTHEMIA
│
├── RELATIVE (Spurious/Apparent)
│   ├── Dehydration (vomiting, diarrhea, burns)
│   ├── Spurious (Gaisböck syndrome): Normal RCM, reduced plasma volume
│   └── Stress polycythemia: obesity, hypertension, smoking
│
└── ABSOLUTE (True - increased total red cell mass)
    │
    ├── PRIMARY (autonomous erythroid proliferation, EPO low/normal)
    │   ├── Polycythemia Vera (PV) - JAK2 V617F mutation
    │   └── Inherited (mutated EPO receptor - rare)
    │
    └── SECONDARY (EPO-driven)
        ├── Appropriate (physiologic hypoxia → ↑EPO)
        │   ├── High altitude
        │   ├── Chronic lung disease (COPD)
        │   ├── Cyanotic congenital heart disease
        │   ├── Carboxyhemoglobinemia (smoking)
        │   ├── High O2-affinity hemoglobins
        │   └── Methemoglobinemia
        │
        └── Inappropriate (non-hypoxic EPO excess)
            ├── EPO-secreting tumors: renal cell carcinoma, hepatocellular carcinoma, cerebellar hemangioblastoma, Wilms tumor
            ├── Polycystic kidneys, renal artery stenosis
            ├── Post-renal transplant
            └── Exogenous EPO ("blood doping")

Polycythemia Vera (PV) - Primary

1. Hb >16.5 g/dL (men) or >16.0 g/dL (women) OR elevated RCM
2. Hypercellular BM with trilineage hyperplasia and pleomorphic megakaryocytes
3. JAK2 V617F or JAK2 exon 12 mutation

• Subnormal serum EPO level

• Primary (PV): Low EPO, JAK2 positive, panmyelosis
• Secondary: High EPO, JAK2 negative, erythroid hyperplasia only

---

Q8. Cytogenetics in Hematologic Malignancies

Why Cytogenetics Matters

• Diagnostic markers (WHO classification often requires cytogenetics)
• Prognostic indicators (favorable vs. unfavorable)
• Therapeutic targets (BCR-ABL → imatinib)
• Monitoring tool (minimal residual disease)

Methods

1. Conventional karyotype (G-banding): 20-25 metaphase cells analyzed; detects translocations, deletions, inversions at band resolution (~10 Mb)
2. Fluorescence in situ hybridization (FISH): Labeled DNA probes hybridize to specific chromosomal loci; detects known abnormalities in both dividing and non-dividing cells; useful for t(9;22), 17p deletion
3. RT-PCR: Detects specific fusion transcripts (BCR-ABL1, PML-RARA) at high sensitivity; used for diagnosis and MRD monitoring
4. Microarray (SNP array/CGH): Detects copy number variations, loss of heterozygosity at high resolution
5. Next-generation sequencing (NGS): Comprehensive mutation profiling (JAK2, NPM1, FLT3, IDH1/2, TP53, etc.)

Key Cytogenetic Abnormalities by Disease

• t(9;22)(q34;q11) - Philadelphia chromosome in virtually 100% of cases
• Creates BCR-ABL1 fusion gene encoding a constitutively active 210-kDa tyrosine kinase (p210)
• Activates Ras, STAT5, PI3K/Akt pathways promoting proliferation and inhibiting apoptosis
• BCR-ABL1 kinase inhibitors (imatinib, dasatinib, nilotinib, ponatinib) are the treatment
• Loss of Philadelphia chromosome is the goal of therapy (major cytogenetic response)
• Additional cytogenetic changes (trisomy 8, isochromosome 17q, double Ph) = blast crisis

• MDS: del(5q), -7, del(7q), del(20q), -17, complex karyotype
• del(5q) MDS: isolated del(5q) = favorable, lenalidomide-responsive
• Myeloproliferative neoplasms: JAK2 V617F, CALR, MPL mutations (molecular, not cytogenetic)

---

Q9. Bone Marrow Failure Syndrome

Definition

Classification

1. Aplastic anemia (most common acquired BMFS)
   • Severe aplastic anemia (SAA): ANC <500/µL, platelets <20,000/µL, reticulocytes <1%
   • Moderate aplastic anemia (MAA)
   • Causes: idiopathic (majority - immune-mediated T-cell destruction), drugs (chloramphenicol, NSAIDs, sulfonamides, gold), radiation, viruses (EBV, CMV, HIV, hepatitis), PNH, pregnancy
2. Pure red cell aplasia (PRCA)
   • Selective absence of erythroid precursors
   • Causes: parvovirus B19 (aplastic crisis in chronic hemolysis), thymoma, CLL, drugs (EPO antibodies)
3. Amegakaryocytic thrombocytopenia
4. Myelophthisis - marrow replacement by fibrosis, metastatic tumor, granulomas

1. Fanconi anemia - autosomal recessive; defects in DNA repair (FANC genes); pancytopenia, skeletal anomalies, café-au-lait spots, increased cancer risk (AML, squamous cell carcinoma)
2. Dyskeratosis congenita - telomerase gene mutations (TERT, TERC, DKC1); skin pigmentation, nail dystrophy, oral leukoplakia
3. Shwachman-Diamond syndrome - SBDS gene mutation; neutropenia + exocrine pancreatic insufficiency
4. Diamond-Blackfan anemia - pure red cell aplasia; ribosomal protein mutations; congenital anomalies
5. Severe congenital neutropenia (Kostmann) - ELANE mutation; severe neutropenia from birth

Pathogenesis of Aplastic Anemia (Immune-mediated)

1. An initial trigger (virus, drug, or occult PNH clone) exposes HSC antigens
2. Oligoclonal expansion of CD8+ cytotoxic T cells (Th1-polarized)
3. Production of IFN-γ and TNF-α by activated T cells → induce Fas-FasL-mediated apoptosis of HSCs and inhibit hematopoietic growth
4. Regulatory T cell (Treg) deficiency allows unchecked immune activation
5. Reduced telomere length in HSCs (some cases have germline telomerase mutations)
6. Result: progressive depletion of all HSC lines → pancytopenia

Laboratory Diagnosis

Diagnosis of Severe Aplastic Anemia (Camitta Criteria)

• Neutrophils <500/µL (very severe: <200/µL)
• Platelets <20,000/µL
• Reticulocytes <1% (or <60,000/µL corrected)

Treatment

• Immunosuppression: anti-thymocyte globulin (ATG) + cyclosporine + eltrombopag
• Allogeneic stem cell transplantation (curative - first line in young patients with matched sibling donor)
• Supportive: RBC/platelet transfusions, G-CSF, antimicrobials

---

Q10. Pancytopenia - Pathogenesis & Diagnostic Approach

Definition

• Red blood cells (anemia: Hb <13 g/dL in men, <12 g/dL in women)
• White blood cells (leukopenia: WBC <4,000/µL; neutropenia: ANC <1,500/µL)
• Platelets (thrombocytopenia: <150,000/µL)

Classification / Causes

• Paroxysmal nocturnal hemoglobinuria (PNH): hemolysis + marrow aplasia

Pathogenesis (Special Emphasis)

• Deficiency of vitamin B12 or folate → impaired thymidylate synthesis → defective DNA replication
• "Maturation arrest": nuclear development lags behind cytoplasmic development (nucleocytoplasmic dissociation)
• Ineffective hematopoiesis: megaloblasts are destroyed in marrow (intramedullary hemolysis) before reaching circulation
• All cell lines affected: macro-ovalocytes, hypersegmented neutrophils, giant platelets, hypercellular marrow despite pancytopenia

• Clonal mutations in hematopoietic stem cells (splicing factors: SF3B1, SRSF2; epigenetic regulators: TET2, DNMT3A, ASXL1; transcription factors: RUNX1)
• Dysplastic (abnormal) cell morphology but ineffective hematopoiesis - cells fail to mature or undergo apoptosis in the marrow
• Peripheral blood pancytopenia with hypercellular or normocellular marrow (ineffective = production present but output absent)

• Marrow space replaced by tumor, fibrosis, or granulomas
• Leukoerythroblastic reaction: release of immature precursors (myelocytes, metamyelocytes, nucleated RBCs) into circulation because normal marrow architecture is disrupted
• Teardrop-shaped RBCs (dacryocytes): hallmark of myelofibrosis

• Enlarged spleen traps and destroys RBCs, WBCs, and platelets
• Marrow is hyperplastic (compensatory) - distinguishes from aplastic anemia
• Pancytopenia is modest (rarely severe)

• Immune-mediated: autoantibodies against RBCs (Coombs positive), platelets, and neutrophils
• Plus bone marrow suppression by inflammatory cytokines

Diagnostic Approach

• Drug/toxin/radiation history (aplastic, MDS)
• Family history (Fanconi, dyskeratosis congenita)
• Duration and symptoms: fatigue, infections, bleeding
• B-symptoms (fever, weight loss, night sweats): lymphoma, TB
• Travel history: Leishmaniasis

• CD59 (protectin) and CD55 (DAF) expression on RBCs and granulocytes
• Absent in PNH clones (PIGA gene mutation)
• PNH clone detected by flow cytometry in ~50% of aplastic anemia; may coexist

---