INTERNATIONAL LP(A) STANDARDIZATION

Two international surveys for Lp(a) measurements were organized from 1989 to 1991. The results of the first survey led to the conclusion that the lack of a common primary standard was the main cause of the large 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 larger number of participants. During the second survey, no consistent effect due to freezing or lyophilization could be demonstrated, although there was a trend towards lower Lp(a) values in lyophilized samples. The inter- and intra-laboratory coefficients of variation did not vary significantly for the different Lp(a) phenotypes, and variability was comparable for lyophilized, liquid and frozen materials. Large intra-assay coefficients of variation were observed during both surveys. Results obtained in different laboratories using the same commercial reagents and standards also showed a large variation. These initial results demonstrate that the lack of a primary standard and poor assay precision are the main factors responsible for the high inter-laboratory variation observed during these surveys.