Determination of von Willebrand factor activity with collagen-binding assay and diagnosis of von Willebrand disease: effect of collagen source and coating conditions.

The collagen-binding assay was recently recommended as the new method for determining von Willebrand factor activity.(1-3) The assay is based on measurement of the quantity of von Willebrand factor molecules bound to collagen, similar to the procedure for an enzyme-linked immunosorbent assay. Many authors have reported problems in efficiently coating microplates with collagen and have suggested special procedures requiring chemical modification of the microplate surface and collagen or a high concentration of this protein and long incubation times.(4,5) Other studies indicate that the reasons for this problem are the origin of the collagen used for coating and the conditions under which the coating procedure is carried out. Modification of coating conditions and the use of an alkaline buffer permits the use of relatively low concentration of collagen, 5 to 10 microg/mL, and allows the test to be completed in one day. This procedure is useful in the diagnosis of von Willebrand disease and allows researchers to distinguish between disease types I and II.