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

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:RCo) 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:RCo, 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:RCo. Linear regression of VWF:Ab and VWF:RCo 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.