Physiology MCQ – Thrombin inhibitor

Which of the following inhibits thrombin activity?

A. Heparin cofactor II

B. Alpha 2 antitrypsin

C. Chymotrypsin

D. Alpha 2 macroglobulin

Correct answer : D. Alpha 2 macroglobulin

Thrombin inhibitors in plasma are:

• Antithrombin III (75% of total activity)
• Alpha 2 macroglobulin
• Heparin cofactor II (minor)
• Alpha 1 antitrypsin (minor)

So both A and D are correct, but the best answer is D (Alpha 2 macroglobulin).