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Diagnostic Tests: Ristocetin Cofactor Assay
Overview — What This Test Is
The Ristocetin Cofactor Assay is a laboratory test that evaluates the functional activity of von Willebrand factor (VWF).
Ristocetin acts as a surrogate for the endothelial surface, promoting VWF-mediated platelet agglutination. When VWF is present and functioning normally, platelets will clump in response to ristocetin.
This assay, together with a VWF antigen level, is considered one of the most accurate tests for diagnosing von Willebrand disease (vWD).
When This Is the Correct Answer
Choose the Ristocetin Cofactor Assay when a patient presents with:
This pattern suggests qualitative VWF defects, particularly Type 2 von Willebrand disease, where VWF quantity may be normal but function is impaired.
The ristocetin assay detects impaired VWF-mediated platelet adhesion, helping distinguish between quantitative and qualitative defects.
Overview — What This Test Is
The Ristocetin Cofactor Assay is a laboratory test that evaluates the functional activity of von Willebrand factor (VWF).
Ristocetin acts as a surrogate for the endothelial surface, promoting VWF-mediated platelet agglutination. When VWF is present and functioning normally, platelets will clump in response to ristocetin.
This assay, together with a VWF antigen level, is considered one of the most accurate tests for diagnosing von Willebrand disease (vWD).
When This Is the Correct Answer
Choose the Ristocetin Cofactor Assay when a patient presents with:
- Platelet-type bleeding, such as:
- Epistaxis
- Petechiae
- Purpura
- Gum bleeding or gingival bleeding
- Normal platelet count
- Normal VWF level, but clinical suspicion for vWD remains
(e.g., VWF is present but non-functional)
This pattern suggests qualitative VWF defects, particularly Type 2 von Willebrand disease, where VWF quantity may be normal but function is impaired.
The ristocetin assay detects impaired VWF-mediated platelet adhesion, helping distinguish between quantitative and qualitative defects.
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