Evaluation of von Willebrand factor activity in factor VIII/von Willebrand factor concentrates with the automated von Willebrand factor: activity IL test.

The von Willebrand ristocetin cofactor assay is still the main cleared measurement test used to evaluate von Willebrand factor (vWF) activity in concentrate samples containing vWF. Although the assay's performance has been improved over the years, the test reliability is still affected by a high interassay and interlaboratory variability; moreover, it requires skilled technicians and significant time. An automated HemosIL vWF:activity test, already set up on plasma samples, was then applied to factor VIII/vWF concentrates to verify its suitability in routine analysis of concentrate samples. As first step precision, linearity and accuracy were assessed. Then, 40 commercial batches of a high purity factor VIII/vWF concentrate were examined with this new method. The Spearman's correlation between the results obtained with the HemosIL vWF:activity assay and vWF activities determined by established procedures was evaluated. Comparisons of the means between HemosIL vWF:activity and the other tests were calculated with the Wilcoxon and Bland-Altman tests. Validation study showed satisfying within-run and between-run precision values. Activities determined with HemosIL vWF:activity had good correlation with those determined as ristocetin cofactor, Imubind (vWF:Imubind) and collagen-binding. Wilcoxon test, used to compare the means between the HemosIL vWF:activity and the other activity assessments, proved no significant variation with vWF:Imubind, but displayed a slight variation with von Willebrand ristocetin cofactor and von Willebrand factor:collagen-binding. This automated HemosIL vWF:activity test could be included in routine determination of vWF activity in concentrate samples and supports traditional von Willebrand ristocetin cofactor because it is reliable, reproducible and sensitive.