Presentation Details
| Clinical Utility and Performance of von Willebrand Factor Activity Assays in a National Reference Laboratory: The Vitalant Coagulation Laboratory’s Experience with the Ristocetin Cofactor and VWF:GP1bM Assays Angela Verdoni1, Mason Marshall2, Irina Chibisov1. 1Vitalant Coagulation Laboratory, Pittsburgh, PA, USA.2Department of Pathology, University of Pittsburgh, Pittsburgh, PA, USA |
Abstract
Background: The Ristocetin Cofactor (RCoF) VWF activity assay has been utilized in the laboratory assessment of von Willebrand Disease for many decades. However, issues with high interlaboratory variability and assay interference have been well described. In the fall of 2022, a new VWF activity assay referred to as the VWF:GP1bM assay was FDA cleared for in vitro diagnostic use. The Vitalant Coagulation Laboratory began offering this assay as a clinical test in early 2023. Objective: To compare performance of the VWF:RCoF activity assay with the VWF:GP1bM activity assay by assessment of results in the context of available clinical and laboratory findings. Methods: Data were extracted from the Vitalant Coagulation Laboratory LIS system for a seven-month period for the following assay results: VWF:RCoF activity, VWF:GP1bM activity, VWF Antigen level, FVIII clotting activity, Collagen/EPI and Collagen/ADP closure times, 1.2mg and 0.3mg ristocetin induced platelet aggregations, Collagen binding activity, and VWF Multimers. Cases were excluded from further analysis if data was not available for the VWF:RCoF activity, VWF:GP1bM activity and VWF Antigen level on the same sample. After exclusion, more than 400 cases were assessed. Each individual case was examined for whether the VWF:GP1bM and VWF:RCoF activity results were in qualitative agreement. Cases with qualitative disagreement were further examined by comparing other VWD test results and clinical histories to make a conclusion whether the VWF:RCoF or the VWF:GP1bM assay made a more accurate assessment of VWF activity. Results: The VWF:GP1bM test yielded higher activity results overall than the VWF:RCoF activity assay. Thirty three percent of cases had a VWF:GP1bM/vW Antigen ratio >0.70 and a VWF:RCoF/vW Antigen ratio <0.70 whereas the reverse was true for only 1% of cases. Fifty percent of the cases analyzed had results that fell within the normal range for both the VWF:RCoF and VWF:GP1bM assays and thus there was no benefit of ordering the VWF:GP1bM activity test. Fourteen percent of cases were in agreement with a known/suspected case of Type 1 VWD based upon low results for the VWF:RCoF, VWF:GP1bM, and vW Antigen assays. Six percent of cases were in agreement with a known/suspected case of Type 2 VWD based upon low results for the VWF:RCoF and VWF:GP1bM assays and normal results for the vW Antigen assay. In 23% of cases, the VWF:GP1bM assay result was normal in the presence of a low RCoF result, making the presence of VWD less likely. However, in 5% of cases, VWF:GP1bM results were normal in the presence of low VWF:RCoF and other abnormal VWD testing and positive clinical history, pointing to a potential for misclassification in these cases. Conclusions: The addition of the VWF:GP1bM activity result in the presence of the VWF:RCoF result was potentially beneficial in ~25% of cases analyzed, had no benefit in ~70% of cases, and may have resulted in a misclassification in ~5% of cases. These data show an overall benefit of ordering VWF:GP1bM activity test and also confirm the notion that no single VWD test is an ideal test for assessment of von Willebrand Disease.
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