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Why Are PT & PTT Normal in Dysfibrinogenemia?

From Tania Puro, first posted on November 14: Can you explain why the activated partial thromboplastin time (APTT, PTT) and the prothrombin time PT are normal in dysfibrinogenemia?

Hello, and thank you for your question. Dysfibrinogenemia is a qualitative or functional fibrinogen deficiency associated with moderate to severe liver disease. The liver produces normal or even elevated fibrinogen levels, but the fibrinogen is coated with excess sialic acid and functions poorly. Liver disease is associated with soft tissue (anatomic) bleeding owing to deficiencies of several coagulation factors. Dysfibrinogenemia plays a role in the bleeding. The thrombin and reptilase clotting time are prolonged, and clot-based Clauss fibrinogen assay results, based on the thrombin time, are reduced. Because dysfibrinogenemia is a functional disorder, fibrinogen assays that rely on nephelometry, such as estimates provided by coagulometers in the performance of a PT, may be normal or elevated.

PT and PTT reagents are designed to be moderately insensitive to hypofibrinogenemia and dysfibrinogenemia, and only become prolonged when fibrinogen concentration or functional levels are below 100 mg/dL, which explains why the PT and PTT may be normal in dysfibrinogenemia.

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