Prothrombin Time (PT) | Blood Test for Clotting Time

Prothrombin time (PT) is a blood test performed to evaluate the coagulation function in patients. Blood clotting has different mechanisms and pathways, and one of them has to do with coagulation factors. Since many of them are synthesized by the liver, PT can help diagnose liver disease.

In this article, we will discuss how this test works, what can be diagnosed with a prothrombin time test, and how results are usually interpreted.

What is Prothrombin time?

Prothrombin time is a useful blood test to assess the coagulation capacity of the blood. That is, the ability to create blood clots and how fast it happens. It is measured in seconds, and what doctors do is taking the blood sample, adding certain substances known as reactants, and waiting for blood clots to form. The number in seconds represents how much it takes for blood clots to form.

Prothrombin time is designed to evaluate the viability of specific proteins known as coagulation factors. There are many coagulation factors, and they are all essential to obtain blood clots. Prothrombin time considers factor number I, II, V, VII, and X. Additional coagulation factors are assessed by a similar test known as partial thromboplastin time, which is often performed simultaneously.

Excessive clotting function causes thrombi in the blood, which block arteries and cause circulation problems. Ineffective clotting causes spontaneous bleeding episodes, which can be very severe depending on the case.

Prothrombin time depends on the reactants used by the laboratory. That’s why it is so important to compare your results with the normal range values provided by the same laboratory.

In some cases, the prothrombin time is used to calculate the Internationalized Normalized Ratio, also known as INR. This is a standardized calculation useful to monitor patients who receive warfarin and other anticoagulants.

Written by Martin Davis