Anti-nuclear antibody (ANA) analysis should include specific analysis of antibodies to SS-A/Ro

Objectives

Evaluation of ELISAs and immunodiffusion (ID) in addition to IF microscopy for ANA screening.

Methods

3079 patient sera sent for routine analysis were diluted 1:100 in PBS and examined by IF microscopy (HEp-2 cells) for the presence of ANA. In addition, all sera were analysed by two different commercial ELISAs for screening of ANA specificity. The sera were also analysed by an in-house ID test for precipitating antibodies to extractable nuclear antigens (ENA). All sera positive in any of the ELISAs or ID were further analysed by an 'ANA profile' ELISA kit and a commercial ID test for determination of antigenic specificity.

Results

334 (11%) of the sera were positive by IF microscopy. 102 (31%) of these sera were also positive in at least one additional test. 214 HEp-2 negative sera (7%) turned out positive in at least one of the additional ANA tests. In 40 of these 214 sera the antigenic specificity was confirmed by the commercial ID test, 37(92%) of which proved to have specificity for SS-A/Ro. The different ELISAs correlated poorly with one another.

Conclusion

In addition to IF-microscopy on HEp-2 cells, an assay for anti-SS-A antibodies should be included for routine ANA screening.