PTT

Background

• Partial thromboplastin time (aPTT); measures the intrinsic and common coagulation pathways
• Used to monitor unfractionated heparin therapy

Normal Values

• Normal: 25-35 seconds
• Therapeutic for heparin: typically 60-80 seconds (1.5-2.5x normal; varies by institution)

Interpretation

• Prolonged by heparin, hemophilia A/B (Factors VIII/IX), von Willebrand disease, DIC, lupus anticoagulant, liver disease
• Lupus anticoagulant prolongs PTT but is paradoxically a risk factor for thrombosis, not bleeding
• Isolated prolonged PTT with no bleeding history: consider lupus anticoagulant or Factor XII deficiency (neither causes clinical bleeding)

See Also

• PT
• INR
• Coagulation Studies
• Heparin