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Test Findings

Prolonged APTT



    • Causes of Prolonged APTT

    • Isolated Prolonged APTT

    • Unfractionated heparin - therapeutic or contamination
    • Overcoagulation with low molecular weight heparin
    • Factor deficiency - VIII, IX, VI, XII
    • Factor inhibitors
    • Von Willebrand disease
    • Lupus anticoagulant (antiphospholipid antibody)
    • Prolonged APTT and PT/INR

    • Artefactual - high haematocrit
    • Liver disease
    • Disseminated intravascular coagulation (DIC)
    • Common pathway deficiency - X, V, II, fibrinogen
    • Severe vitamin K deficiency
    • Excess heparin (e.g. from heparin in the line)
    • Warfarin
    • Factor IIa inhibitors (dabigatran)
    • Factor Xa inhibitors (rivaroxaban, apixaban)
    • Approach

    • Determine whether the patient is on heparin or any other anticoagulants.
    • Check the patient’s haematocrit, which if elevated will falsely elevate PT/INR and APTT.
    • Look for evidence of chronic liver disease, either in the patient’s past medical history or current clinical state.
    • Assess the patient’s risk of DIC given their clinical state.
    • If unsure about the cause of prolonged APTT, mixing studies can be performed.
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