Which treatment is associated with prolonged prothrombin time and normal or mildly prolonged partial thromboplastin time, with platelets unaffected?

• A. Aspirin
• B. Warfarin
• C. Heparin
• D. Vitamin K

Answer: (B)

Warfarin produces a pattern where the extrinsic pathway is slowed more than the intrinsic pathway. It does this by blocking vitamin K–dependent synthesis of factors II, VII, IX, and X. Because factor VII has the shortest half-life, the prothrombin time (PT) rises first and is prolonged, while the partial thromboplastin time (PTT) stays normal or only mildly prolonged early on. Platelet numbers stay unaffected because warfarin does not directly impair platelets. This combination of prolonged PT with normal or only mildly prolonged PTT and normal platelets is characteristic of warfarin therapy. In contrast, aspirin affects platelets and doesn’t typically alter PT/PTT in this pattern; heparin mainly lengthens PTT; vitamin K deficiency would also affect both pathways and isn’t described as a treatment pattern.