Blood Thinning Monitor (PT/INR) - Prothrombin Time (PT) and INR Test

The prothrombin time (PT) test with International Normalized Ratio (INR) is a blood test that measures the time required for a clot to form in a plasma sample after the addition of tissue thromboplastin and calcium. It primarily assesses the efficiency of the extrinsic and intrinsic pathways in the coagulation cascade (factors VII, X, V, II, and fibrinogen). The INR is calculated from the PT value to compensate for variations between different laboratory reagents, making it a globally accepted standard for monitoring vitamin K antagonist (warfarin) therapy.