Summary

Despite the widely recognized practical importance of anticardiolipin(aCL) ELISA, the reliability of this test has been recently discussed.In order to investigate this area on European scale, we sent to 30 experiencedcenters a questionnaire focusing on the diagnostic proceduresapplied to patients with antiphospholipid syndrome (APS) and on thedetailed protocols used to perform aCL. Anticardiolipin ELISA wasfound to be the most frequently performed test in patients with suspectedAPS, but significant difference was shown among the various protocols.The cross-laboratory multiple examination of ten serum samplesevaluated independently by the 24 centers pointed out the difficulty ingetting comparable results. Therefore a “consensus” protocol was derivedfrom the aCL methods giving the best performance. The materi-alsand reagents necessary to perform the “consensus” method, including,as putative standards, one IgG and one IgM monoclonal antibody(HCAL and EY2C9) were distributed to 19 Centers. The results of oneIgG and one IgM aCL high positive sera measured in serial dilutionswere compared. A progressive decrease in the variability of the valuesobtained for a given sample appeared evident when all the laboratoriesused the same standard, in their own in-house ELISA and even more inthe “consensus” ELISA.Our data show that aCL ELISA standardization is necessary in orderto obtain comparable results in different laboratories.