Warfarin initially degrades proteins C and S before factors II, IX, and X. This creates a transient hypercoagulable state early in therapy. Which of the following best explains why protein C depletion causes thrombosis before the anticoagulant effect of warfarin is evident?
- A Protein C is a natural anticoagulant with a short half-life, so its levels drop before factors II, IX, and X ✓
- B Protein C is a procoagulant zymogen activated by thrombin
- C Protein C has a longer half-life than factor II
- D Protein C activates factor V, amplifying coagulation when depleted
Correct answer: A. Protein C is a natural anticoagulant with a short half-life, so its levels drop before factors II, IX, and X
Explanation
Protein A is a vitamin K-dependent natural anticoagulant with a short half-life (~6-8 hours), whereas factor II (prothrombin) has a long half-life (~60-72 hours). Early warfarin therapy depletes protein A faster than factors II, IX, and X, causing a transient prothrombotic state. Skin necrosis is a recognized early complication. Protein A is anticoagulant, not procoagulant.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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