Comparison of different kits in the detection of autoantibodies to cardiolipin and beta2glycoprotein 1.

OBJECTIVE: To estimate the performance characteristics of 10 commercial kits and one in-house kit for the detection and quantification of anticardiolipin (aCL) (six kits) and anti-beta2glycoprotein 1 (anti-beta2GP1) (five kits) antibodies, and to evaluate the degree of variability between these different kits.
METHODS: We determined the presence of aCL and anti-beta2GP1 IgG and IgM antibodies in 67 sera from 62 patients and reviewed the data separately. Each serum sample was tested with six commercial aCL determination kits and with four commercial and one in-house anti-beta2GP1 determination kit. We then analysed the operating characteristics of each kit (sensitivity, specificity, positive and negative predictive values) and we analysed the absolute and 2 x 2 agreements.
RESULTS: The 62 patients included had primary antiphospholipid syndrome (APS) in 10 cases, secondary APS for eight, systemic lupus (SLE) for 23 and other diagnoses for the remaining 21. Operating characteristics differed from one kit to another. Good agreement was found using sensitive aCL determination kit and specific anti-beta2GP1 determination kit. Agreement between kits was medium for IgG aCL. 2 x 2 concordance studies showed a group of three aCL kits which were quite homogenous and showed that all anti-beta2GP1 kits formed quite a homogenous group.
CONCLUSION: A high degree of variability still persists for aCL antibody determination posing the question of the qualification of commercial or in-house kits and the question of standardization of results. A better concordance is found for high positive results. Good agreement exists for anti-beta2GP1 kits. aCL determination is still needed and should be complemented by anti-beta2GP1 determination.