Test Findings
 

Prolonged INR

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Overview

    • Causes of Prolong PT/INR

    • Isolated Prolonged PT/INR

    • Warfarin (low dose)
    • Mild vitamin K deficiency
    • Factor VII deficiency
    • Prolonged PT/INR and APTT

    • Artefactual - high haematocrit
    • Liver disease
    • Disseminated intravascular coagulation (DIC)
    • Common pathway deficiency - X, V, II, fibrinogen
    • Severe vitamin K deficiency
    • High dose heparin
    • Warfarin
    • Factor IIa inhibitors (dabigatran)
    • Factor Xa inhibitors (rivaroxaban, apixaban)
    • Approach

    • Determine whether the patient is on warfarin 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 PT/INR, mixing studies can be performed.
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