An ELISA test for the binding of von Willebrand antigen to collagen.

Collagen (soluble bovine tendon type I) coated onto microtiter plates binds von Willebrand antigen (vW:Ag) in a dose-dependent manner. An ELISA test was set up with both antibody and collagen coated microtiter plates. Test specimens assayed were: 1) normal plasmas, 2) type I vW plasmas, 3) type IIa vW plasmas, and 4) factor VIII concentrates (KoateR, Cutter; Conco-VIII, Green Cross). Normal and type I vW plasmas exhibited comparable values for vW:Ag in binding studies to both collagen and antibody-coated plates. Type IIa vW plasmas demonstrated decreased (less than 1/2) collagen to antibody-binding ratios. Ristocetin cofactor (VIII:RCO) levels in type IIa vW plasmas correlated with quantified collagen-binding levels. Factor VIII concentrates show variable results when comparing collagen and antibody-binding levels. A comparison of vW:Ag ELISA (antibody) with VIII:RCO shows ratios of 2:1 (KoatR) or 20:1 (Conco-VIII). Collagen-binding ELISA levels in concentrates show parallel decreases, reflecting presumed binding to collagen of only the high M.W. multimers. The vW:Ag collagen binding ELISA represents a possible replacement assay for the laborious and imprecise VIII:RCO method of measurement of in vitro vWf functional activity.