Activated Partial Thromboplastin Time (aPTT): Purpose, Interpretation, and Causes of Prolongation

The aPTT test measures the time (in seconds) for plasma to clot after adding phospholipid and an activator. It evaluates the intrinsic and common coagulation pathways.

Clinical Uses

• Screening for coagulation disorders (e.g., hemophilia, von Willebrand disease)
• Monitoring unfractionated heparin therapy
• Preoperative coagulation assessment

Causes of Prolonged aPTT

• Vitamin K deficiency
• Liver disease
• Disseminated intravascular coagulation (DIC)
• Antiphospholipid antibody syndrome
• Heparin, warfarin, direct oral anticoagulants
• Factor deficiencies (VIII, IX, XI, XII)
• Pregnancy (physiologic shortening may occur)

An elevated aPTT warrants further investigation to identify the underlying etiology.