Background: Type 2 variants of congenital von Willebrand disease (VWD) and acquired VW syndrome (AVWSyn) typically have an abnormal VWF multimers (VWFM): decreased or loss of high molecular weight VWF multimers (HMWM)). A VWF activity (VWF:Ab) to VWF antigen (VWF:Ag) ratio of <0.7 raises suspicion of congenital Type 2 VWD, in acquired AVWSyn the ratio may be higher and the VWF levels are typically normal.

Aims: For patients with normal VWF levels (≥55%), to determine prevalence of abnormal VWFM at a VWF:Ab to VWF:Ag ratio cut off of 0.7 or 0.8.

Methods: Retrospective analysis of VWD test panels between March and September 2019. ROC analysis of VWF:Ab to VWF:Ag ratio of <0.8 vs <0.7 for abnormal VWFM was conducted.

Results: Over the study period, of a total 5,340 VWD panels, 1735 were reflexed to VWFM analysis based on a cut off of <0.8 of which 1065 had normal VWF levels. Of those with ratio 0.7-0.8 (n=845), 45 (5%) had abnormal VWF. Of the 212 with ratio <0.7, 97 (46%) had an abnormal VWFM. Optimal cut-off to diagnostic accuracy assessed with ROC analysis comparing the ratio to qualitative VWFM interpretation. Data set 1, all panels reflexed to VWFM (n=1735), acheived optimal threshold of 0.620, AUC at 0.834. Data set 2, panels with normal VWF levels (n=1065), acheived optimal threshold of 0.620, AUC at 0.836.

Figure 1

Conclusions: There is a higher prevalence of abnormal VWFM at a VWF:Ab to VWF:Ag ratio cut off of 0.7  and is consistent with recent VWD guidelines for type 2 VWD and AVWSyn. The latter patients with normal VWF levels, may still have abnormal VWFM and thus may need follow up VWFM testing.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/correlation-of-vwfab-to-vwfag-ratio-and-abnormal-vwf-multimer-pattern/