Which statement about fibrinogen testing methods is true?

• A. The two main fibrinogen tests are functional (Clauss) and antigen assays
• B. Only Clauss assay is used
• C. Fibrinogen testing is not used in coagulopathy
• D. Fibrinogen testing is primarily a platelet function test

Answer: (B)

Fibrinogen testing uses two complementary approaches to capture different aspects of the protein’s role in clot formation. The functional assessment, typically done with the Clauss method, measures how well fibrinogen can support a clot. It does this by triggering polymerization with an excess of thrombin and recording the time to clot formation. This functional readout is particularly useful for detecting qualitative defects in fibrinogen, such as dysfibrinogenemia, where the amount may be normal but the function is impaired.

The antigen, or immunologic, assay quantifies how much fibrinogen protein is present in the plasma. It tells you the concentration, independent of whether the molecule is functioning properly. This is important for identifying true shortages of fibrinogen (hypofibrinogenemia) or monitoring replacement therapy, but it does not directly assess functional activity.

In practice, both tests are used because patients can have discordant results—normal fibrinogen levels with impaired function, or low levels with preserved function. Relying on only one approach could miss clinically relevant abnormalities. The other statements aren’t accurate: fibrinogen testing is indeed used in evaluating coagulopathy, and it is not a platelet function test.