Which lab test is critical for monitoring women on warfarin during pregnancy?

• A. PT (Prothrombin Time)
• B. INR (International Normalized Ratio)
• C. APTT (Activated Partial Thromboplastin Time)
• D. HGB (Hemoglobin)

Answer: (B)

The International Normalized Ratio (INR) is the critical lab test for monitoring women on warfarin during pregnancy because it provides a standardized measure of how long it takes for blood to clot, which is particularly important when a patient is on anticoagulation therapy. Warfarin works by inhibiting vitamin K-dependent clotting factors, and the INR helps ensure that the level of anticoagulation is within a therapeutic range that balances the risks of clotting versus bleeding.

During pregnancy, women may undergo physiological changes affecting coagulation, and maintaining appropriate anticoagulation is crucial to minimize risks to both the mother and the fetus. The INR is preferred because it is adjusted for variability between different laboratories, providing a consistent way to assess anticoagulation levels, which is vital when managing patients on warfarin.

Other tests listed can provide important information but do not serve as the primary monitoring tool for warfarin therapy. For instance, Prothrombin Time (PT) is related to INR and may provide some information, but INR is the standardized form derived from PT that is used clinically. Activated Partial Thromboplastin Time (APTT) is more relevant for monitoring heparin therapy, while Hemoglobin (HGB) levels may help assess