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PA20.1-2 | DIC & Vitamin K Deficiency — Part 2
Clinical Features of DIC
Clinical Features of Disseminated Intravascular Coagulation
The clinical picture reflects the dual pathology of thrombosis and haemorrhage:
Haemorrhagic manifestations:
• Bleeding from multiple sites simultaneously — venepuncture sites, IV cannulas, surgical wounds, mucous membranes
• Ecchymoses and purpura
• Haematuria, haemoptysis, gastrointestinal bleeding in severe cases
Thrombotic manifestations (often subclinical):
• Microthrombi in kidneys → acute tubular necrosis, oliguria/anuria
• Microthrombi in lungs → ARDS
• Microthrombi in brain → encephalopathy, seizures
• Purpura fulminans: haemorrhagic necrosis of skin from dermal vessel thrombosis — a dramatic and grave sign
Key clinical rule: bleeding from at least three unrelated sites in a critically ill patient should prompt urgent DIC screen. The underlying trigger must be treated simultaneously — treating DIC without treating sepsis or delivering the placenta is futile.
Acute DIC presents with dramatic haemorrhage. Chronic DIC (e.g., from metastatic carcinoma or giant haemangioma — Kasabach-Merritt syndrome) may present insidiously with deep vein thrombosis and mild lab abnormalities.
Laboratory Findings in DIC — The Classic Panel
Classic Laboratory Panel in Acute DIC
The DIC laboratory panel is one of the most important diagnostic panels in clinical pathology. Learn it as a complete pattern:
| Test | Typical finding in acute DIC | Why |
|---|---|---|
| Platelet count | ↓ (< 100 × 10⁹/L) | Consumed in microthrombi |
| PT | ↑ (prolonged) | Factors II, V, VII, X consumed |
| aPTT | ↑ (prolonged) | Factors V, VIII, fibrinogen depleted |
| Fibrinogen | ↓↓ (< 1.0 g/L in severe DIC) | Consumed; fibrinogen is an acute-phase reactant so even a "normal" level may be low relative to expected baseline |
| D-dimer | ↑↑ (markedly elevated) | Secondary fibrinolysis of cross-linked fibrin |
| FDPs | ↑↑ | Fibrinolysis products; inhibit further fibrin polymerisation |
| Peripheral blood film | Schistocytes (fragmented RBCs) | MAHA from fibrin-strand shearing |
ISTH scoring system (simplified): Platelet count, PT prolongation, fibrinogen level, and D-dimer are scored 0-2 each. A score ≥ 5 is consistent with overt DIC. The score is also used to track treatment response.
Chronic DIC: D-dimer and FDPs are elevated, fibrinogen may be normal or high (compensated), platelets may be low-normal.
DIC Laboratory Panel: Key Tests and Pathophysiology
CLINICAL PEARL
D-dimer vs FDPs — know the difference: D-dimer is a fibrin-specific degradation product (from cross-linked fibrin) and is the more specific DIC marker. FDPs include both fibrinogen and fibrin breakdown products — they are sensitive but less specific. A very high D-dimer with elevated FDPs strongly supports secondary fibrinolysis in DIC. In primary fibrinolysis (rare, e.g., thrombolytic overdose), FDPs are elevated but D-dimer is low-to-normal because cross-linked fibrin is not the primary substrate. This distinction matters in examinations.
Schistocytes and MAHA in DIC
⚑ AI image — pending faculty review (auto-QA score 7/10; best of 3 attempts)
Schistocytes and MAHA in DIC
Red cell fragmentation occurs when erythrocytes are mechanically sheared by fibrin strands stretched across microvascular lumens. The resulting fragments — schistocytes (also called helmet cells or fragmented red cells) — are visible on the peripheral blood film as irregular, helmet-shaped, or triangular red cell remnants.
In DIC, the combination of:
• Schistocytes on film
• Thrombocytopenia
• Elevated LDH and falling haemoglobin
…constitutes microangiopathic haemolytic anaemia (MAHA). MAHA is not unique to DIC — recall from H5 that TTP and HUS also produce MAHA. The distinguishing features are:
• DIC: PT and aPTT both prolonged, fibrinogen ↓, D-dimer ↑↑
• TTP: coagulation tests NORMAL (schistocytes + thrombocytopenia without PT/aPTT prolongation)
• HUS: predominantly renal failure, often follows diarrhoeal illness
Schistocytes in DIC-Associated MAHA and Fibrinolysis Comparison
SELF-CHECK
A patient with DIC has a peripheral blood film showing fragmented red cells, a platelet count of 45 × 10⁹/L, and a markedly elevated D-dimer. Which finding most specifically confirms secondary fibrinolysis rather than primary fibrinolysis in this case?
A. Elevated FDPs
B. Prolonged aPTT
C. Markedly elevated D-dimer with low fibrinogen
D. Schistocytes on peripheral smear
Reveal Answer
Answer: C. Markedly elevated D-dimer with low fibrinogen
D-dimer is a fragment generated specifically from the plasmin degradation of cross-linked fibrin (i.e., fibrin that has already been incorporated into a clot and factor XIIIa-cross-linked). A markedly elevated D-dimer combined with low fibrinogen (consumed in clot formation) confirms that clotting occurred first (generating cross-linked fibrin) and fibrinolysis followed — this is secondary fibrinolysis as seen in DIC. In primary fibrinolysis (plasminogen activator excess), FDPs are high but D-dimer is NOT elevated because primary fibrinolysis degrades fibrinogen, not already cross-linked fibrin.