Which diagnostic test is commonly used to monitor warfarin therapy?

• A. Complete Blood Count (CBC)
• B. Prothrombin time (PT) and International Normalized Ratio (INR)
• C. Liver Function Tests
• D. Electrolytes Panel

Answer: (B)

The International Normalized Ratio (INR) is a critical tool for monitoring patients on warfarin therapy due to the medication's narrow therapeutic index and its potential for significant interaction with various factors. Warfarin acts as an anticoagulant by inhibiting vitamin K-dependent clotting factors that are essential for the coagulation cascade. The prothrombin time (PT) measures how long it takes for blood to clot and provides insight into the effectiveness of warfarin in prolonging this time.

The INR is specifically derived from the PT value and standardizes it based on the sensitivity of the reagent used in the test, allowing for consistent monitoring across different laboratories. Regularly checking INR ensures that patients remain within the therapeutic range, minimizing the risks of both thromboembolic events and bleeding complications. This makes PT and INR the standard tests for assessing the adequacy of anticoagulation with warfarin, and adjustments in dosage can be made based on these values to maintain proper anticoagulation levels.

The other tests mentioned do not serve this monitoring purpose. A Complete Blood Count (CBC) provides information on blood cell levels but does not assess coagulation. Liver Function Tests can indicate whether the liver is functioning properly, which is indirectly related but