What is the reference range for prothrombin time (PT)?

• A. 12.6-14.6 seconds
• B. 9-11 seconds
• C. 15-18 seconds
• D. 7-9 seconds

Answer: (A)

Prothrombin time reflects how long it takes for blood to clot via the extrinsic and common pathways, mainly involving factors II, V, VII, and X. Because the result is a time in seconds, different labs set a reference window based on their thromboplastin reagents and equipment, but a common normal range is about 11–15 seconds. The interval 12.6–14.6 seconds falls well within that typical normal range, making it a normal PT value. Values shorter (e.g., 9–11 seconds) would indicate faster clotting, while values longer (e.g., 15–18 seconds) suggest prolongation and potential coagulation abnormalities or anticoagulant effects. Keep in mind that PT is often used alongside INR when monitoring anticoagulation therapy like warfarin.