Prothrombin Time Test

Prothrombin Time, commonly abbreviated PT and usually reported alongside a standardized value called INR (International Normalized Ratio), measures how long it takes your blood to form a clot.

This test specifically evaluates the function of several clotting factors that are produced by the liver and depend on vitamin K, making it useful both for assessing liver function and for monitoring blood-thinning medications like warfarin.

INR was developed specifically to standardize PT results across different laboratories and testing reagents worldwide, which is essential for patients on long-term warfarin therapy who might have their blood tested at different labs over time.

Beyond medication monitoring, PT is also a routine part of pre-surgical clotting assessments and is used to investigate unexplained bleeding or bruising.