Analysis of the multimeric composition of vWF is required for accurate classification of vWD subtypes. Several methods of quantifying vWF activity have been described. 31 Ristocetin cofactor assay with fixed normal platelets is normal in the plasma of patients with Bernard-Soulier syndrome. Another method for measuring vWF activity is by collagen binding assay.
Patient plasma is added to pepsin-digested type III collagen immobilized on microtiter wells.
Ag level as type O plasma. Some laboratories have developed different normal ranges for each blood type. Since vWF is an acute-phase reactant, levels are increased during stress, pregnancy, and in the newborn after vaginal delivery. Reduced plasma vWF may be found in patients who are hypothyroid, but their levels return to normal when they become euthyroid. 36 Substrate plasmas that have been immunodepleted of factor VIII have also been used but may give abnormal results because vWF is also removed during the immunodepletion.