Validation of automated latex von Willebrand factor activity assay in a new prospective study including post‐treatment patient samples

Summary Introduction Von Willebrand disease ( VWD ) is the most prevalent inherited bleeding disorder. Diagnosis requires measurement of VWF –platelet binding function, for which VWF ristocetin cofactor activity ( VWF : RC o) is the reference method. Recently, an automated latex particle‐enhanced immunoturbidimetric von Willebrand factor activity assay ( VWF :Ab) has been validated showing superior characteristics. We further validate VWF :Ab in a prospective study including post‐treatment patient samples. Methods A total of 1151 samples were collected from patients tested for VWD , including 119 samples from patients treated with desmopressin or VWF replacement product. All samples were tested for VWF :Ab and VWF : RC o, and the methods were compared using linear regression. Imprecision, linearity and lower detection limit were determined for both assays. Results VWF :Ab showed improved precision compared to VWF : RC o. Linear regression of VWF :Ab and VWF : RC o across all samples exhibited good agreement (R 2 = 0.89) with statistical significance ( P < 0.001) and bias of −8.7. Concordance was high in classifying samples as normal or abnormal. Analysis of treated samples showed excellent agreement (R 2 = 0.91) with statistical significance ( P < 0.001) and bias of −4.3. Conclusions Our analysis validates the VWF :Ab assay in a prospective study of a large cohort of patient samples and extends these results to post‐treatment patient samples.