Hemostasis Coagulation Practice Test 2026 – All-in-One Guide to Mastering Your Exam!

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In the Clauss fibrinogen assay, the time to clot formation in plasma is measured after the addition of which reagent?

Calcium

Thrombin

The Clauss fibrinogen assay relies on directly triggering fibrin formation with an excess of thrombin. By adding thrombin to plasma, it rapidly converts whatever functional fibrinogen is present into fibrin, so the time to clot mainly reflects the amount of functional fibrinogen. Calcium and phospholipids may be present to support the reaction, but they are not the initiating trigger. Fibrin is the product, not the reagent added. Therefore, the reagent added to initiate clotting is thrombin.

Phospholipids

Fibrin