Which test is used to confirm a diagnosis of warfarin (rodenticide) toxicity?

• A. Thrombocyte count
• B. One-step prothrombin time
• C. Calcium level
• D. Partial thromboplastin time

Answer: (B)

Warfarin toxicity diverts the coagulation system by inhibiting vitamin K–dependent clotting factors (II, VII, IX, X), which mainly impacts the extrinsic pathway. The test that best detects this specific pathway defect is the one-step prothrombin time, because it directly measures the clotting ability of the extrinsic pathway using tissue factor. A prolonged prothrombin time (often standardized as an INR) indicates that coagulation is impaired due to vitamin K antagonist exposure, making it the most sensitive and appropriate test to confirm warfarin (rodenticide) toxicity. The partial thromboplastin time assesses the intrinsic pathway and is less consistently affected early in vitamin K antagonist poisoning; calcium level and platelet count do not specifically diagnose this toxicity.