Clinically relevant differences between assays for von Willebrand factor activity

Abstract

It is unclear whether there are differences between von Willebrand factor (VWF) activity assays. We compared the four most used VWF activity assays in 661 von Willebrand disease (VWD) patients. All assays correlated excellently, but a discrepant classification was seen in 20% of patients. Differences between VWF activity assays have a large impact on the classification of VWD. Summary BackgroundMeasuring the ability of von Willebrand factor (VWF) to bind to platelets is crucial for the diagnosis and classification of von Willebrand disease (VWD). Several assays that measure this VWF activity using different principles are available, but the clinical relevance of different assay principles is unclear. ObjectiveTo compare the four most widely used VWF activity assays in a large VWD patient population. MethodsWe measured VWF:RCo (ristocetin to activate VWF + whole platelets), VWF:GPIbR (ristocetin + platelet glycoprotein Ib receptor [GPIb] fragments), VWF:GPIbM (gain‐of‐function GPIb fragments that bind VWF spontaneously without ristocetin) and VWF:Ab (monoclonal antibody directed against the GPIb binding epitope of VWF to mimic platelets) in 661 VWD patients from the nationwide ‘Willebrand in the Netherlands’ (WiN) Study. ResultsAll assays correlated excellently (Pearson r > 0.9), but discrepant results led to a different classification for up to one‐fifth of VWD patients. VWF:RCo was not sensitive enough to classify 18% of patients and misclassified half of genotypic 2B VWD patients, especially those with p.Arg1306Trp. VWF:GPIbR was more sensitive, accurately classified the vast majority of patients, and was unaffected by the p.Asp1472His variant that causes artificially low VWF:RCo. VWF:GPIbM was the most precise assay but misclassified over a quarter of genotypic 2A, 2B and 3 patients. VWF:Ab, often not considered an actual VWF activity assay, performed at least equally to the other assays with regard to accurate VWD classification. ConclusionAlthough the different VWF activity assays are often considered similar, differences between assays have a large impact on the classification of VWD.

von Willebrand factor and factor VIII levels after desmopressin are associated with bleeding phenotype in type 1 VWD

“…Moreover, for different VWF activity assays, we recently reported that they are generally very comparable to each other in patients with type 1 VWD. 34 In conclusion, VWF and FVIII levels after desmopressin administration, which mimic in vivo hemostatic response to hemostatic challenges, are associated with the bleeding phenotype of patients with type 1 VWD. The clinical relevance of this association is highlighted by our findings that patients with the highest VWF and FVIII levels 3 hours after desmopressin administration had a 5-point lower bleeding score, and patients with FVIII:C in the highest quartile had ;10 times lower chance of presenting with an abnormal bleeding score.…”

Diagnostic challenges of inherited mild bleeding disorders: a bait for poorly explored clinical and basic research

“…Although not yet widely available, this assay appears to be the most precise tool for measuring VWF activity . A recent report comparing four different VWF activity assays confirmed the precision of VWF:GPIbM; however, it misclassified a significant proportion of genotype 2A, 2B and 3 patients . This assay, and the ristocetin‐dependent VWF:GPIbR, based on a recombinant GPIb fragment captured by a plate‐coated mAb, are insensitive to the VWF variant p.Asp1472His, which results in misleadingly 25% lower VWF:RCo values .…”

How I manage severe von Willebrand disease

“…Due to the fact that the originally developed assay is elaborate and time consuming, has a poor sensitivity and high variation, several new activity tests have been developed in recent years (Bodo et al , ; Boender et al , ). In a recent study, the four currently most widely used VWF activity assays were compared in a cohort of 661 well‐defined VWD patients (Boender et al , ). The assays were found to be highly correlated with each other.…”

“…The VWF:RCo assay, using ristocetin to activate VWF and whole platelets, was not sensitive enough to classify 18% of the total study population and misclassified half of the genotypically identified 2B patients. Also the VWF:GPIbM test, using gain‐of‐function GPIb fragments that bind spontaneously to VWF, misclassified some definite type 2 and type 3 VWD patients (Boender et al , ).…”

“…We also perform mutation analysis in VWD type 2 patients, to enable the diagnosis of, or exclude, VWD in their unborn child by amniotic fluid sampling at 32–34 weeks of pregnancy and to assess whether an atraumatic delivery is necessary. We also perform genetic testing for scientific purposes, for instance in the Willebrand in the Netherlands (WiN) study (Boender et al , ).…”