A comparison of two macroscopic platelet agglutination assays for von Willebrand factor.

Plasma drawn from 22 patients with a broad range of von Willebrand factor (vWF) levels, including one patient with rare, severe type III von Willebrand's disease, was used to investigate the adaptability of the Bio/Data Corp. vW Factor Assay, a ristocetin cofactor-based kit developed for use with a platelet aggregometer, to a macroscopic platelet agglutination technique. The results were compared to those obtained using the General Diagnostics von Willebrand Factor Assay, another ristocetin cofactor-based kit developed for use as a macroscopic platelet agglutination procedure. No significant difference (p greater than 0.5) existed between results obtained by these two kits. The mean and standard deviation of the vWF levels (as percent of normal) were 132 +/- 66.7 by the General Diagnostics kit and 133 +/- 59.0 by the Bio/Data Corp. kit. The correlation coefficient (r) was 0.81. The Bio/Data Corp. kit is more costly per test than the General Diagnostics kit. However, it was shown to be compatible with the macroscopic agglutination technique and required no modification to be used in that manner.