[The laboratory diagnosis of von Willebrand's disease (author's transl)].

This investigation was undertaken in order to determine the most suitable methods for diagnosing von Willebrand's disease (v. W. d.), with particular reference to "mild" cases. 50 healthy persons, 21 patients with "severe" v.W.d. (verified according to all hitherto-established criteria) and 39 persons suffering from "mild" v.W.d. were examined. Even though - as far as the latter group is concerned - some of the characteristic laboratory findings were absent, the fact that these persons are related to the patients with "severe" v.W.d. made verification of the diagnosis nevertheless possible. In the group with "mild" v.W.d. 85% had decreased functional factor VIII activity and 82% showed reduced platelet adhesiveness; a prolonged bleeding time according to Borchgrevink was recorded in 72% of the cases and 64% had pathological values for the Ristocetin-induced platelet aggregation were pathological in less than 50% of the group. There was a close relation between the diagnostic significance and reproducibility of the various methods; in regard to the group of patients with "mild" v.W.d., the methods yielding the greatest number of pathological findings (functional factor VIII and platelet adhesiveness) were the ones with the lowest variation coefficients, i.e. 3.1 and 2.1%, respectively. The consideration of a time-dependent rise in the aggregation capability of washed platelets with Ristocetin was of decisive importance in the reproducibility of the rather sophisticated technique of determining the Ristocetin cofactor. The addition of EDTA largely inhabited this effect. Even in the group of patients with "severe" v.W.d., part of the findings obtained with screening tests of the intrinsic coagulation system remained within the normal range. There was no statistical correlation between the individual laboratory findings in the group of healthy persons. In the group with "mild" v.W.d., there was a significant correlation between platelet adhesiveness and Ristocetin-induced platelet aggregation on the one hand, and platelet adhesiveness and the Ristocetin cofactor on the other. In addition, a verified correlation was found to exist between Ristocetin-induced platelet aggregation and Ristocetin cofactor and between functional factor VIII and factor VIII-related antigen. In the group of "severe" v.W.d., only platelet adhesiveness and functional factor VIII were not significantly correlated, whilst all other correlations were of statistical significance. Further problems involved in the diagnosis of v.W.d., such as the variablility of laboratory findings, the existence of subgroups, as well as the difficulties involved in the statistical evaluation of individual cases suffering from v.W.d. are discussed.