An evaluation of the trends in analytical performance of international apolipoprotein A-1 and B assays.

Two international apolipoprotein A-1 and B (apoA-1 and apoB) surveys were conducted in 1983 and 1986 with use of a lyophilized serum measured by 55 and 91 participants, respectively. The chief source of variability in both surveys was among laboratories, but among-method variation was significant for apoB. Comparing the 1986 with the 1983 findings, we saw a 60% decrease in apoA-1 variability among laboratories, and a similar decrease (53%) was found for apoB. Evaluation of individual measurements suggests that some collaborators may have adjusted their calibrators toward the consensus values published in 1983.