Normal prothrombin time (PT) range?

• A. 5-7 sec
• B. 11-15 sec
• C. 20-25 sec
• D. 30-35 sec

Answer: (B)

Normal prothrombin time reflects the function of the extrinsic pathway and vitamin K–dependent coagulation factors. In healthy individuals, PT falls within about 11 to 15 seconds using common laboratory reagents and instruments. This range can vary slightly between labs, but values in this window are considered normal. PT is prolonged when the extrinsic pathway is impaired or factors II, VII, or X are deficient or inhibited, such as with warfarin therapy, vitamin K deficiency, liver disease, or disseminated intravascular coagulation. Therefore, 11–15 seconds is the typical normal PT range.