MULTICENTER EVALUATION OF 9 COMMERCIAL KITS FOR THE QUANTITATION OF ANTICARDIOLIPIN ANTIBODIES

The performances of nine commercial kits and an in-house method (HM) f or the quantitation of anticardiolipin antibodies (ACA) have been eval uated in a multicenter study. Ninety control and patient samples and s ix standards from Louisviile University were run with kits and with th e HM. Marked differences in positivity rate between kits were observed , ranging from 31 to 60% for IgG and 6 to 50% for IgM. Concordance bet ween kits occurred in 59 and 51% of samples for IgG and IgM respective ly. Concordance coefficients (kappa) ranged from 0.13 to 0.92. Slopes of regression lines between the declared units of Louisville standards end the units measured from the calibrators of the kits showed great diversity and ranged from 0.159 to 0.931 for IgG and from 0.236 to 0.8 36 for IgM. The beta(2)-glpcoprotein I (beta(2)-GPI) content of the di lution buffers and the wells supplied with the kits revealed noticeabl e differences. However samples containing anti-beta(2)-GPI antibodies were classified similarly by all but one kit. In contrast the ability to measure samples devoid of anti-beta(2)-GPI antibodies differed mark edly between the kits. This study shows that differences in positivity rates between the commercial kits may contribute to the differences i n ACA prevalence rate found in the literature. The choice of cut-off l evels may partly explain the moderate concordance between the kits. In addition some samples behave very differently depending on the kits. In spite oi tile expression of results in PL units, standardization of ACA assays has not been achieved.