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Kamlesh Darji: A Practical Guide to Interpreting Coagulation Tests
Kamlesh Darji/X
Aug 26, 2026, 17:52

Kamlesh Darji: A Practical Guide to Interpreting Coagulation Tests

Kamlesh Darji, Senior Resident in the Department of Pathology at AIIMS (All India Institute of Medical Sciences), shared a post on X:

“He four core patterns

  • Prolonged APTT with normal PT : hemophilia A/B, factor 11 or 12 deficiency, lupus anticoagulant; vWD may prolong APTT if factor 8 is reduced
  • Prolonged PT with normal APTT : factor 7 deficiency, early warfarin effect, early vitamin K deficiency, early liver disease
  • Both PT and APTT prolonged : DIC, severe liver disease, severe vitamin K deficiency, common pathway factor deficiency
  • Both PT and APTT normal with bleeding : platelet function disorder, mild vWD, factor 13 deficiency, vascular disorder

Mixing study: The Splitter

  • Corrects on mixing : factor deficiency
  • Does not correct on mixing : inhibitor such as lupus anticoagulant or specific factor inhibitor
  • Factor 8 inhibitor : may initially correct but fail to correct after incubation because the inhibitor is time dependent

Platelet disorders

  • Low platelets with large young platelets and normal/increased marrow megakaryocytes : immune thrombocytopenia
  • Low platelets with schistocytes and normal coagulation tests : TTP or HUS
  • Low platelets with schistocytes and deranged coagulation tests : DIC
  • Platelet fall typically 5–10 days after heparin with thrombosis : heparin-induced thrombocytopenia
  • Usually normal platelet count with reduced VWF antigen/activity : von Willebrand disease
  • Reduced ristocetin-induced platelet agglutination corrected by normal plasma : von Willebrand disease
  • Reduced ristocetin-induced platelet agglutination not corrected by normal plasma : Bernard-Soulier syndrome
  • Normal ristocetin response with defective aggregation to ADP, epinephrine and collagen : Glanzmann thrombasthenia
  • Giant platelets with thrombocytopenia : Bernard-Soulier syndrome
  • Small platelets with eczema and immunodeficiency : Wiskott-Aldrich syndrome

Factor deficiencies

  • Factor 8 deficiency : hemophilia A, X-linked
  • Factor 9 deficiency : hemophilia B, X-linked
  • Factor 11 deficiency : hemophilia C, classically associated with Ashkenazi Jewish ancestry
  • Factor 12 deficiency : markedly prolonged APTT without clinical bleeding
  • Factor 13 deficiency : normal PT and APTT with delayed bleeding; diagnose with factor 13 activity assay
  • Vitamin K-dependent factors : 2, 7, 9, 10, protein C and protein S
  • Shortest half-life among vitamin K-dependent clotting factors : factor 7, therefore PT rises first

Highest Yield Information

  • Warfarin-induced skin necrosis : rapid fall in protein C, especially in underlying protein C deficiency
  • Arterial or venous thrombosis with recurrent pregnancy morbidity : antiphospholipid syndrome
  • Prolonged APTT that fails to correct on mixing with thrombosis : lupus anticoagulant
  • Thrombosis with intravascular hemolysis and cytopenias : paroxysmal nocturnal hemoglobinuria
  • Heparin resistance : consider antithrombin deficiency, although several acquired causes also occur
  • Homocystinuria with thrombosis : cystathionine beta-synthase deficiency

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