An enzyme-linked immunosorbent assay (ELISA) for von Willebrand factor antigen (vWf-Ag) in canine plasma

A quantitative enzyme-linked immunosorbent assay (ELISA) has been developed to measure canine von Willebrand factor antigen (vWf-Ag) in plasma of the dog. A vWf-Ag antiserum was raised in rabbits and purified by preabsorption with the low molecular weight vWf-Ag-deficient fraction of canine cryoprecipitate, followed by affinity chromatography on protein-A Sepharose. The rabbit anticanine vWf-Ag IgG was used to bind the vWf-Ag of the test plasmas to the solid phase and to prepare the enzyme-antibody conjugate in ELISA. Normal rat serum was used as blocking agent. The standard curve was linear (r2 greater than 0.98) and reproducible after logit-log transformation. The interassay coefficient of variation (CV) in test plasmas with various vWf-Ag concentrations was never greater than 7.7%. Assayed values in dilutions of pooled normal canine plasma added to canine vWf-Ag-deficient plasma were linear between 0 and 100% (r2 = 0.99) and indicated excellent analytical recovery of vWf-Ag. In 18 dogs with various internal diseases, including von Willebrand's disease and haemophilia A, the coefficient of correlation between the results of the ELISA and those of electroimmunodiffusion (EID) was 0.93.