Why it's done

Most often, the prothrombin time is monitored if you are taking the blood-thinning medication warfarin. In this situation, the prothrombin time is expressed as an international normalized ratio (INR).

Your doctor may recommend a prothrombin time test prior to surgery if there is any concern about your blood's ability to clot.

The prothrombin time test may also be performed to evaluate you for liver disease. It is one of several tests used to screen people waiting for liver transplants. That screening — known as the model for end-stage liver disease (MELD) — is a scoring system for assessing the severity of chronic liver disease.

If your doctor suspects you have other health issues, such as liver problems or a bleeding disorder, you might need additional testing to confirm your condition.