A COMPARATIVE-STUDY OF 6 COMMERCIAL LIPOPROTEIN(A) ASSAYS IN 17 LABORATORIES WITHIN THE BRITISH-ISLES

Seventeen laboratories in the British Isles participated in a study to compare six different commercially available immunoassays for serum l ipoprotein(a) (Lp(a)) and to establish reasons for the variations in t he measurement of serum Lp(a) concentrations. Pooled serum was distrib uted neat and after dilution at a central laboratory. In addition, the central laboratory sent unpooled serum sampled monthly from six healt hy volunteers to each of the participating laboratories for 12 months. The assays all gave linear dilution curves which were parallel, altho ugh the reported values varied twofold. There were major differences i n the values assigned to different manufacturers' calibrants which was not explained by whether the units employed were whole Lp(a), the pro tein moiety of Lp(a) or simply apolipoprotein(a). The coefficient of v ariation for the reported value of Lp(a) over 12 months was 33%. The c omponent variation was 10% after adjustment for inter-laboratory and i ntra-laboratory variation. Some individuals clearly had a greater tend ency to variable serum Lp(a) concentrations than others, but all the a ssays responded to this in the same way. Thus, the assays tested proba bly measured the same analyte. The problem of calibration could largel y be addressed if agreement were reached by the manufacturers. Even wi th improvements in analytical precision it should be realized that mul tiple measurements of serum Lp(a) levels are necessary if the true mea n value is to be appreciated. Individuals showing wide variation in se rum Lp(a) may reward further study if its role is to be established.