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

Why This Test Matters

PT/INR is a critical blood test that evaluates the efficiency of your clotting system. It converts your lab result into a standardized INR value, which doctors use to compare results across different labs and treatments. This is especially important for people on blood thinners, as it ensures their medication is at the right level to prevent clots or bleeding.

How the Test Works

Blood is drawn and mixed with a special solution that triggers the clotting process. The time it takes for a clot to form is measured. The INR adjusts this time to reflect how your blood clots compared to a healthy person’s blood, accounting for differences in lab equipment and reagents.

What to Expect Before the Test

No special preparation is needed unless your doctor instructs otherwise. You may be asked to fast for 12 hours before the test, but this is less common for PT/INR. Wear a comfortable shirt with sleeves rolled up, as you’ll need to expose your arm for the blood draw.

What the Results Mean

Results are reported as a single number (PT) or two numbers (PT/INR). The PT is the time in seconds it takes for your blood to clot, while the INR is a ratio that compares your PT to a healthy person’s. Your doctor will interpret these results in the context of your medical history and any medications you’re taking.