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DOI: 10.1055/s-0038-1646040
Calibration of Lyophilized Standards for Ristocetin Cofactor Activity of von Willebrand Factor (vWF) Requires vWF-Deficient Plasma as Diluent for Dose-Response Curves
Publication History
Received 14 January 1987
Accepted after revision 13 July 1987
Publication Date:
29 June 2018 (online)
Summary
Calibration of local standards for ristocetin cofactor activity of von Willebrand’s factor (vWF : Rcof) against reference preparations is required to achieve a better standardization of this measurement. We have observed that in calibration assays (multiple line parallel bioassay) for vWF : Rcof, measured aggregometrically, the type of diluent used to obtain the dose-response curves exerted a critical influence on the final potency estimation when a fresh-frozen plasma against a lyophilized standard or two lyophilized preparations were to be compared. This pattern was observed with various commercial standards and also with the First International Reference Preparation for Factor VIII-Related Activités in Plasma. The choice of diluent was not relevant if two fresh-frozen plasma preparations were to be calibrated. Systematic experiments using as diluents Trissaline, Tris-buffered-albumin solution or vWF-deficient plasma (vW-plasma) showed that the ratio lyophilized/fresh-frozen preparations was invariably lower with albumin solution than with vW-plasma. Tris-saline partially corrected this discrepancy, but yielded less precise estimates. Preliminary results with cryosuper-natant-plasma seems to indicate that this material is a valid substitute for vW-plasma, but confirmatory experiments are required For the moment, plasma obtained from patients with severe type III vW-disease should be considered the “ideal” diluent for calibration assays involving lyophilized preparations.