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 #Abnormal #PT #aPTT #Prolonged #Causes #diagnosis #differential #hematology #coagulation
