Curriculum · Hematology
Differential diagnosis of a prolonged APTT
What it is
A prolonged aPTT is a result to be worked out, not a diagnosis. The differential divides first by whether the aPTT is prolonged on its own or together with the PT.
Causes and risk
Isolated aPTT prolongation:
- Deficiency of a coagulation factor in the intrinsic pathway
- Contact factor deficiency
- A circulating anticoagulant (inhibitor)
- Lupus anticoagulant
Prolonged PTT with PT:
- Massive transfusion of PRBC
- Disseminated intravascular coagulation
- Liver disease
- Direct thrombin inhibitors
- Thrombolysis
- Combined factor deficiency
- Common pathway factor deficiency
Causes of a prolonged PTT without bleeding include early contact factor (factor XII, HMWK, PK) deficiency, lupus anticoagulant, inappropriate blood draw, heparin contamination and erythrocytosis as a laboratory artifact.