Four Agglutination Assays Evaluated for Measurement of von Willebrand Factor (Ristocetin Cofactor Activity)

The concentration of von Willebrand factor (vWf) in patients’ plasma can be determined by measuring the nstocetin cofactor activity (vWf R:Co). However, this vWf R:Co assay is time consuming, which limits its routine use. Several commercial vWf R:Co tests, based on agglutination of lyophilized fixed platelets, are available. We evaluated the slide tests and aggregometer assays from Behring and Organon Teknika and compared them with the classic vWf R:Co aggregometer method. The within-run and between-run precisions of the two slide tests were better than those of the aggregometer methods. The correlation studies be-tween the four commercial assays and the classic aggre-gation method were based on 23 plasma samples (range: 15-450 % vWf R:Co). The correlation coefficients, which ranged from 0.923 to 0.950, did not differ significantly (P>0.1). All four commercial assays gave significantly lowe