Prolonged APTT
April 24th, 2019
Overview
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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