Bleeding Disorders: Classification and Diagnostic Tests

Introduction

Classification of Bleeding Disorders

1. Vessel Wall Abnormalities

• Vitamin C deficiency (scurvy) — collagen defects weaken vessel walls
• Amyloidosis — amyloid deposition in blood vessel walls
• Ehlers-Danlos syndrome — inherited connective tissue disorder
• Chronic glucocorticoid use — acquired vascular fragility, particularly in older adults ("senile purpura")
• Infections — meningococcemia, rickettsioses, and septicemia cause microvascular damage or vasculitis
• Drug-induced hypersensitivity vasculitis — immune complex deposition in vessel walls
• Henoch-Schönlein purpura — IgA-mediated leukocytoclastic vasculitis

2. Platelet Disorders

A. Thrombocytopenia (Quantitative Defects)

B. Qualitative Platelet Defects

• Bernard-Soulier syndrome — deficiency of GpIb/IX (platelet adhesion receptor for vWF)
• Glanzmann thrombasthenia — deficiency of GpIIb/IIIa (fibrinogen receptor for aggregation)
• Uremia — acquired platelet dysfunction (guanidinosuccinic acid accumulates and impairs platelet activation)
• Aspirin/NSAIDs — irreversible/reversible inhibition of COX → impaired thromboxane A₂ synthesis

3. Coagulation Factor Disorders

Von Willebrand Disease (vWD)

• Type I (most common): Quantitative reduction of vWF; autosomal dominant
• Type II: Selective loss of high-molecular-weight multimers (most active form); types IIA and IIB
• Type III: Severe quantitative deficiency; autosomal recessive; severe bleeding resembling hemophilia

Hemophilia A (Factor VIII Deficiency)

• Severe: <1% activity → spontaneous hemarthroses, deep muscle bleeds
• Moderate: 1–5% activity → bleeding with minor trauma
• Mild: 5–30% activity → bleeding only with significant trauma or surgery

Hemophilia B (Factor IX Deficiency — Christmas Disease)

Hemophilia C (Factor XI Deficiency)

4. Combined / Acquired Disorders

Disseminated Intravascular Coagulation (DIC)

1. Microvascular thrombosis → ischemia of brain, kidneys, adrenals, lungs
2. Consumption of platelets and clotting factors + fibrinolysis activation → severe hemorrhagic diathesis

• Sepsis (endotoxin stimulates tissue factor expression on monocytes/endothelium)
• Major trauma, burns, extensive surgery
• Obstetric complications (amniotic fluid embolism, abruptio placentae, retained dead fetus)
• Malignancy (especially acute promyelocytic leukemia, pancreatic/lung adenocarcinomas)
• Antigen-antibody complexes (SLE, transfusion reactions)

Liver Disease

Vitamin K Deficiency

Laboratory Tests for Diagnosis

1. Prothrombin Time (PT) / INR

• What it tests: Extrinsic and common pathways (factors VII, X, V, II, fibrinogen)
• Method: Plasma + tissue thromboplastin (brain extract) + Ca²⁺ → clotting time in seconds
• Prolonged in: Factor VII, X, V, II, or fibrinogen deficiency; vitamin K deficiency; liver disease; warfarin; early DIC; lupus anticoagulant (sometimes)
• Expressed as INR (International Normalized Ratio) for warfarin monitoring standardization
• Normal PT: ~11–15 seconds

2. Partial Thromboplastin Time (PTT / aPTT)

• What it tests: Intrinsic and common pathways (factors XII, XI, IX, VIII, X, V, II, fibrinogen)
• Method: Plasma + kaolin (contact activator of factor XII) + cephalin (platelet phospholipid substitute) + Ca²⁺ → clotting time in seconds
• Prolonged in: Hemophilia A (factor VIII↓), hemophilia B (factor IX↓), hemophilia C (factor XI↓), factor XII deficiency (no bleeding), heparin therapy, DIC, lupus anticoagulant
• Normal aPTT: ~25–35 seconds

3. Platelet Count

• Method: Electronic particle counter on anticoagulated (EDTA) blood; must be confirmed by peripheral blood smear (PBSM) to exclude clumping artifact
• Reference range: 150,000–450,000/µL (some sources: 150–350 × 10³/µL)
• Thrombocytopenia: <150,000/µL
• Thrombocytosis: >450,000/µL (reactive vs. myeloproliferative)

4. Peripheral Blood Smear (PBS)

• Confirms platelet count accuracy
• Detects schistocytes (fragmented RBCs) in TTP/HUS/DIC — key finding in MAHA
• Large platelets suggest peripheral destruction (ITP, TTP)
• Giant platelets in Bernard-Soulier syndrome

5. Bleeding Time

• Historically used to assess platelet function and vascular integrity in vivo
• A small standardized incision is made in the forearm; time to cessation is measured
• Prolonged in: Thrombocytopenia, qualitative platelet defects (vWD, aspirin, uremia, Glanzmann thrombasthenia, Bernard-Soulier syndrome)
• Now largely abandoned — time-consuming, difficult to standardize, poor predictive value for surgical bleeding; replaced by PFA-100

6. Platelet Function Analyzer (PFA-100 / Closure Time)

• In vitro simulation of primary hemostasis; measures time for platelet plug to occlude a collagen/ADP or collagen/epinephrine membrane under high shear stress
• Prolonged closure time in vWD, aspirin use, platelet receptor defects
• More reproducible than bleeding time; useful screening test for platelet dysfunction

7. Platelet Aggregation Studies

• Platelets are exposed to agonists: ADP, collagen, thrombin, arachidonic acid, ristocetin
• Aggregation response measured by light transmittance (platelet-rich plasma turbidimetry) or impedance
• Ristocetin-induced platelet aggregation (RIPA):
  • Absent in vWD type I/IIA (insufficient vWF)
  • Enhanced at low ristocetin concentrations in vWD type IIB (hyperfunctional vWF)
  • Absent in Bernard-Soulier syndrome (absent GpIb receptor)
• Absent aggregation to all agonists except ristocetin → Glanzmann thrombasthenia (GpIIb/IIIa deficiency)

8. von Willebrand Factor Tests

9. Specific Clotting Factor Assays

• Chromogenic or one-stage clotting assays measure activity of individual factors
• Essential for confirming hemophilia: Factor VIII assay (hemophilia A), Factor IX assay (hemophilia B)
• Mixing study: Patient plasma mixed 1:1 with normal plasma:
  • PTT corrects → factor deficiency (hemophilia)
  • PTT does not correct → inhibitor present (factor VIII inhibitor, lupus anticoagulant)

10. D-Dimer and Fibrin Degradation Products (FDPs)

• Products of plasmin-mediated fibrin cleavage
• D-dimer: Specific for cross-linked fibrin degradation (elevated in DIC, DVT/PE, sepsis)
• FDPs (includes X, Y, D, E fragments): elevated in DIC and primary fibrinolysis
• D-dimers and FDPs are elevated in 80–90% of acute DIC cases
• Inhibit platelet aggregation, fibrin polymerization, and thrombin → perpetuate coagulopathy

11. Fibrinogen Level

• Synthesized in liver; consumed in DIC and primary fibrinolysis
• Low fibrinogen (<150 mg/dL) in DIC, liver failure, primary fibrinolysis, dysfibrinogenemia
• Elevated as an acute-phase reactant in many other conditions

12. Thrombin Time (TT)

• Measures conversion of fibrinogen → fibrin by adding exogenous thrombin to plasma
• Prolonged in: Hypofibrinogenemia, dysfibrinogenemia, heparin therapy, DIC (FDPs interfere), dabigatran
• Useful to distinguish fibrinogen defects from other coagulopathies

13. Bone Marrow Biopsy

• Evaluates megakaryocyte number and morphology
• Increased megakaryocytes → peripheral platelet destruction (ITP, TTP, hypersplenism)
• Decreased megakaryocytes → reduced production (aplastic anemia, marrow infiltration)

14. Flow Cytometry for Platelet Glycoproteins

• Directly quantifies GpIb (CD42b) and GpIIb/IIIa (CD41/CD61) on platelet surface
• Confirms Bernard-Soulier syndrome (absent CD42b) and Glanzmann thrombasthenia (absent CD41/CD61)

15. ADAMTS13 Activity and Inhibitor Assay

• Reduced ADAMTS13 activity (<10%) confirms TTP
• ADAMTS13 inhibitor (autoantibody) confirms acquired TTP; its absence suggests hereditary form

16. Genetic Testing

• Molecular analysis for specific mutations in factor VIII gene (hemophilia A — intron 22 inversion most common), factor IX gene, vWF gene
• Used for carrier detection and prenatal diagnosis

Diagnostic Algorithm Summary

Suspected bleeding disorder
        ↓
Clinical history: pattern of bleeding (mucocutaneous vs. deep), 
onset (congenital vs. acquired), family history, drug history
        ↓
First-line tests: PT, PTT, Platelet count, PBS
        ↓
┌───────────────────────────────────────────────────┐
│ Isolated prolonged PTT, normal PT                  │
│ → Factor VIII, IX, XI assay + mixing study         │
│ → vWF studies if mucocutaneous bleeding            │
├───────────────────────────────────────────────────┤
│ Isolated prolonged PT, normal PTT                  │
│ → Factor VII deficiency, early vitamin K deficiency│
├───────────────────────────────────────────────────┤
│ Both PT and PTT prolonged                          │
│ → DIC (+ D-dimer, fibrinogen, FDPs)                │
│ → Liver disease, severe vitamin K deficiency       │
│ → Common pathway factor deficiency (V, X, II)      │
├───────────────────────────────────────────────────┤
│ Low platelet count, normal PT/PTT                  │
│ → PBS for schistocytes                             │
│ → Bone marrow biopsy                              │
│ → ADAMTS13 if TTP suspected                       │
├───────────────────────────────────────────────────┤
│ Normal all tests, clinical bleeding present        │
│ → PFA-100, platelet aggregation, vWF studies       │
│ → Vessel wall disorder (clinical/biopsy)           │
└───────────────────────────────────────────────────┘

Conclusion

• Robbins & Kumar Basic Pathology, 10th ed. (Elsevier) — Chapter 10: Bleeding Disorders, pp. 426–431
• Robbins, Cotran & Kumar Pathologic Basis of Disease, 10th ed. — Chapter 14: Bleeding Disorders, pp. 618–627
• Recent literature: Mehic et al. (2024), "Utility of Global Hemostatic Assays in Patients with Bleeding Disorders of Unknown Cause," Hämostaseologie [PMID: 38950624]; Gresele et al. (2025), "Investigation of Bleeding Disorders: When and How Should We Test Platelet Functions?" Hämostaseologie [PMID: 40355112]