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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