INTERNATIONAL LP(A) STANDARDIZATION

Two international surveys for Lp(a) measurements were organized from 1 989 to 1991. The results of the first survey led to the conclusion tha t the lack of a common primary standard was the main cause of the larg e inter-laboratory variation observed. No major effects of techniques or antisera were observed. The same findings were confirmed during the second survey, which was extended to include more samples and a large r number of participants. During the second survey, no consistent effe ct due to freezing or lyophilization could be demonstrated, although t here was a trend towards lower Lp(a) values in lyophilized samples. Th e inter- and intra-laboratory coefficients of variation did not vary s ignificantly for the different Lp(a) phenotypes, and variability was c omparable for lyophilized, liquid and frozen materials. Large intra-as say coefficients of variation were observed during both surveys. Resul ts obtained in different laboratories using the same commercial reagen ts and standards also showed a large variation. These initial results demonstrate that the lack of a primary standard and poor assay precisi on are the main factors responsible for the high inter-laboratory vari ation observed during these surveys.