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Von Willebrand Disease (VWD)
Part 3: VWF Activity Assay

A New von Willebrand Factor Activity Assay and Testing Algorithm

Comparison of VWF:Lx/Ag and VWF:RCo/Ag Ratios

Slide 15

June 2011

Let us look at the distribution of the VWF latex activity over antigen ratio in different sample categories. The normal cut off is 0.7 as indicated by the red line. A vast majority of the normal samples had normal VWF latex over antigen ratios with rare outliers. All 57 type 1 von Willebrand disease samples had normal VWF latex activity ratios.

Twenty-eight of the thirty-one type 2A or 2B samples had abnormal ratios with only 3 outliers. All 4 2M VWD samples had abnormal ratios. We can not really compare the 2 methods in the group of severe types 1 vs 2M when VWF ristocetin cofactor activity is below lower detection limit. Finally, and interestingly, of the 24 samples with subtle losses of the highest molecular weight multimers, VWF latex activity ratios were significantly lower than those of the VWF ristocetin cofactor activity, and subsequently more sensitive for detecting such an acquired VWF abnormality. Occasional discrepant VWF ristocetin cofactor activity over antigen ratios were also observed.

Comparison of Ratios


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