Differential Diagnosis for a Prolonged PT and aPTT
If the PT and the aPTT are both prolonged, there could be multiple factors affected in the intrinsic and extrinsic pathways or a single factor deficiency in the common pathway: FX, FV, Fll or severe fibrinogen deficiency.
Causes include :
1. Pre-analytical cause (e.g. heparin contamination, under filling of tube)
2. Drugs: Direct or indirect inhibitory drugs (e.g. direct thrombin inhibitors, heparin), Supratherapeutic warfarin effect (FII, FVII, FIX, FX < 30%)
3. Inhibitors: Non specific inhibitor (e.g. antiphospholipid antibodies), Specific inhibitors to the common pathway factors (rare)
4. Decreased factor synthesis :
• Congenital deficiency
• Reduced liver synthesis (impaired production Fll, FV, FVII, FIX, FX, FXII, FXIII, dysfibrinogenemia)
• Severe vitamin K deficiency (↓FII, FVII, FIX, FX)
5. Factor consumption or binding
• Massive hemorrhage
• Disseminated intravascularcoagulation (DIC)
• Factor X deficiency associated with systemic amyloidosis
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