Effect of the Polymorphic Variant p.D1472H on the Platelet‐Dependent VWF Activity Assays

BACKGROUND: The von Willebrand factor (VWF) p.D1472H variant has been shown to artificially lower ristocetin cofactor (VWF:RCo) levels because of impaired VWF binding to ristocetin. Understanding the variant's effect on platelet-dependent VWF activity assays is crucial for avoiding over- or misdiagnosis of von Willebrand disease. AIM: To determine whether p.D1472H affects the VWF:GPIbR latex immunoassay (LIA). METHODS: We investigated 150 subjects for VWF:Ag and platelet-dependent VWF activity using four commercially available assays: VWF:GPIbR LIA, VWF:GPIbR chemiluminescence immunoassay (CLIA), VWF:RCo automated, and VWF:GPIbM LIA. p.D1472H was detected directly using Sanger sequencing or as part of other projects using next-generation sequencing (NGS). RESULTS: A total of 106 subjects were homozygous for aspartic acid [p.D1472H (-)], 41 heterozygous, and 3 homozygous for histidine [p.D1472H (+)]. Using VWF:RCo, p.D1472H (+) subjects (n = 44) showed a significantly lower median VWF activity/VWF:Ag ratio than p.D1472H (-) subjects (p < 0.0001). No significant difference for this ratio was observed between the two groups when assessed using VWF:GPIbR LIA (p = 0.63). Similarly, no significant difference was observed in the presence or absence of the variant (p = 0.31) for the VWF:GPIbR CLIA. Using VWF:GPIbM, a significant difference (p = 0.00052) was observed between the two median ratios. CONCLUSIONS: Our results for the first time show that VWF:GPIbR LIA, despite using ristocetin, is not affected by p.D1472H; hence, it offers reliable results to differentiate VWF quantitative from qualitative deficiencies. We further confirmed that VWF:RCo is highly compromised by p.D1472H, while VWF:GPIbR CLIA is unaffected. VWF:GPIbM LIA results were significantly lower in the p.D1472H (+) subjects than those in p.D1472H (-).