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Table 102.2

Acquired Causes of Prolonged Prothrombin Time (PT) and Activated Partial Thromboplastin Time (APTT)

PTAPTTCause
ProlongedNormalWarfarin or other vitamin K antagonist therapy
Vitamin K deficiency
Liver disease
Acquired factor VII deficiency
Inhibitor of factor VII
NormalProlongedHeparin therapy
Inhibitors of factors VIII, IX, XI or XII
Acquired von Willebrand disease (usually associated with autoimmune or clonal proliferative disorders)
Lupus anticoagulant (associated with thrombosis)
ProlongedProlongedLiver disease
Disseminated intravascular coagulation
Excess heparin
Excess warfarin or other vitamin K antagonist therapy (ingestion of rat poison)
Heparin+warfarin therapy
Primary amyloidosis-associated factor X deficiency
Inhibitors of prothrombin, fibrinogen or factors V or X
VariableVariableThe direct-acting oral anticoagulants (dabigatran, rivaroxaban and apixaban) have variable effects on the PT and APTT, depending on the drug, its concentration (the dose-response is not always linear) and the particular laboratory assay. If you have a patient taking one of these drugs who is bleeding, always consult a haematologist. A reversal agent for dabigatran is now available (idarucizumab). See Chapter 103.