Prothrombin Time (PT) with International Normalized Ratio (INR) – Serum/Plasma

What Is PT/INR Testing Used For?

PT/INR is primarily used to evaluate the effectiveness of blood thinners (anticoagulants) like warfarin and to screen for or monitor conditions affecting blood clotting, such as liver disease or clotting factor deficiencies. It’s also part of routine checks for patients at risk of bleeding or those with inherited clotting disorders.

How Is the Test Performed?

A small blood sample is drawn from a vein, typically in your arm. The blood is mixed with a special reagent to measure how long it takes to form a clot. The INR is calculated to standardize results across different labs.

What Does a PT/INR Result Mean?

Results are reported as a time (usually in seconds) and an INR value. A higher PT or INR may indicate slower clotting, which could signal bleeding risks or liver issues. A lower PT/INR might suggest faster clotting, raising concerns about clotting disorders or overuse of blood thinners.

Common Conditions Affecting PT/INR

Elevated PT/INR is often seen in liver disease (since clotting factors are produced there), vitamin K deficiency, or use of anticoagulants. Low PT/INR may occur with clotting disorders, severe dehydration, or rare genetic conditions.