Which of the following coagulation disorders is associated with an increased risk of thrombosis due to a deficiency of a naturally occurring anticoagulant?

A Protein S deficiency
B Antithrombin III deficiency ✓
C Factor XIII deficiency
D Plasminogen activator inhibitor-1 deficiency

Explanation

Antithrombin III is a naturally occurring anticoagulant that inhibits the activity of thrombin and other coagulation factors. A deficiency of antithrombin III can lead to an increased risk of thrombosis.

Source

Harrison's Principles of Internal Medicine
Hematology Hematology: Coagulation Disorders Hematology: Coagulation Disorders Hard MEDICAL Confidence: high