Which test is used to measure the time it takes for blood to clot?

Prothrombin time (PT) is a specific laboratory test that measures the time it takes for blood to clot. This test evaluates the extrinsic pathway of coagulation and is particularly useful for monitoring patients on anticoagulant therapy, such as warfarin. PT is reported in seconds and can also be expressed as an International Normalized Ratio (INR), which standardizes results regardless of the testing method used by different laboratories.

The other tests listed serve different purposes. A complete blood count (CBC) provides an overview of various blood components, including red and white blood cells and platelets, but does not measure clotting time. The platelet count determines the number of platelets in the blood, which are essential for the clotting process but do not directly indicate the time it takes for blood to clot. Fibrinogen level measures the concentration of fibrinogen, a protein crucial for blood clot formation, but like the platelet count, it does not assess the actual clotting time. Thus, PT is the appropriate test for evaluating the time needed for blood to clot.