A prothrombin time test measures how quickly your blood clots. Sometimes called a PT or pro time test.
A blood sample from arm vein.
Prothrombin time test results can be presented in two ways.
The average time range for blood to clot is about 10 to 14 seconds. A number higher than that range means it takes blood longer than usual to clot. A number lower than that range means blood clots more quickly than normal.
This ratio — which allows for easier comparisons of test results from different laboratories — is used if you take blood-thinning medications.
In healthy people an INR of 1.1 or below is considered normal. An INR range of 2.0 to 3.0 is generally an effective therapeutic range for people taking warfarin for disorders such as atrial fibrillation or a blood clot in the leg or lung. In certain situations, such as having a mechanical heart valve, you might need a slightly higher INR.
When the INR is higher than the recommended range, it means that your blood clots more slowly than desired, and a lower INR means your blood clots more quickly than desired.