An international collaborative study on standardization of apolipoproteins A-I and B. Part I. Evaluation of a lyophilized candidate reference and calibration material.
We evaluated a lyophilized serum preparation for use as a candidate Reference Material for apolipoproteins (apo) A-I and B. An international collaborative study was conducted with 28 participating laboratories, selected on the basis of participation and demonstrated expertise in a 1983 survey of apolipoproteins A-I and B. The analytical suitability of the material was established by confirming linearity of its dose-response curves over a desired concentration range and demonstrating that its response curves paralleled those for fresh sera. Differences in dilution-adjusted mass units ascribable to the five analytical methods used by the various laboratories constituted only 1% of the total variation for apo A-I, but 32% for apo B. The dominant source of error, however, for both apo A-I and B was the variability among laboratories, rather than variability among methods and antisera. The assigned consensus mass-concentration units based on study data are 1.124 g/L for apo A-I, 0.589 g/L for apo B. For these estimates the coefficients of variation were 13% and 27%, respectively. These findings on the proposed Reference Material meet the requirements suggested by the World Health Organization's Expert Committee on Biological Standards for a candidate WHO Reference Preparation.