Prothrombin Time/International Normalized Ratio

Prothrombin Time (PT)
is the most common way to express the clotting tendency of blood. PT results are reported as the number of seconds the blood takes to clot when mixed with a thromboplastin reagent.

The International Normalized Ratio (INR) was created by the World Health Organization because PT results can vary depending on the thromboplastin reagent used. The INR is a conversion unit that takes into account the different sensitivities of thromboplastins. The INR is widely accepted as the standard unit for reporting PT results.

Why Regular PT/INR Monitoring is Important
The effectiveness of oral anticoagulants can vary over time, as changes in diet, (particularly foods high in vitamin K), alcohol use, other drugs and illness can all affect PT. These factors require that the PT is monitored regularly so the patient stays within the desired therapeutic range. Oral anticoagulant dosages are then adjusted according to the results of the PT test.

Furthermore, several studies have shown that the more time patients spend within the desired range of INR the less likely they are to suffer serious complications of their disease or condition.

Learn about PT/INR Point of Care Testing >>