Step 3 UWSA Practice Exam

Starting warfarin requires knowing how your blood clots now and whether your organs that influence drug handling are functioning properly. The liver synthesizes the vitamin K–dependent clotting factors that warfarin ultimately reduces, so checking liver function helps anticipate how strongly the INR may rise and how risky bleeding could be. A baseline INR is important because you’ll be using INR to guide dosing once therapy begins, so knowing the current coagulation status provides a reference point for future monitoring. A complete blood count is needed to assess platelets and baseline anemia, both of which raise bleeding risk if you anticoagulate. Kidney function is checked because renal disease is common in patients with atrial fibrillation and can affect overall management and bleeding risk, even though warfarin itself is primarily metabolized by the liver. Lipid panel, potassium, and thyroid function aren’t routinely required solely to start warfarin, as they don’t directly determine initial dosing or immediate bleeding risk in the way the above tests do.