[The anti-dsDNA antibodies: validation of an original two step strategy of detection]

Detection of anti-dsDNA antibodies is one of the major biological criteria of use in the diagnosis of systemic lupus erythematosus. Sensitivity and specificity vary greatly between existing techniques, and differ largely from one study to another. The aim of our prospective study was to evaluate a new strategy of detection comprising two steps, first, the use of a sensitive automated technique, ELISA Phadia EliA™, and second, if necessary, a more specific technique: the Crithidia luciliae immunofluorescence test (CLIFT). The latter was used in case of discrepancy with previous laboratory findings or according to the available clinical data. During the study period of 18 months, 1729 tests were requested of which 96 were finally assayed using CLIFT. Analysis of 53 discordant results showed 14 cases of lupus identified only with ELISA, and 3 only by Crithidia. In addition, 35 likely false positives of ELISA were evidenced by negative CLIFT results. These data show a clear gain in sensitivity without any loss of specificity due to the use of a second technique. Thus, this strategy was validated in our lab; it can be useful by any medical laboratory because the cost of few Crithidia luciliae slides is very low.