INR (International Normalized Ratio) and PT (Prothrombin Time) are closely related, but they differ in how they’re used and standardized: 1. Prothrombin Time (PT): PT measures the time (in seconds) it takes for blood to clot. Usually 11-13.5 sec. It’s specifically testing the extrinsic pathway of the coagulation system, which involves certain clotting factors (e.g., Factors I, II, V, VII, and X). PT results can vary between labs due to differences in testing methods and reagents. So… 2. Internat