PT
Background
- Prothrombin time; measures the extrinsic and common coagulation pathways (Factors VII, X, V, II, fibrinogen)
- Usually reported alongside INR
Normal Values
- Normal: 11-13.5 seconds
Interpretation
- Prolonged by warfarin, liver disease, vitamin K deficiency, DIC, factor deficiencies
- In practice, INR is used more commonly than raw PT seconds
- PT prolonged first (before PTT) in early liver disease or warfarin therapy because Factor VII has the shortest half-life (~6 hours)