Immunofluorescence microscopy is superior to fluorescent beads for detection of antinuclear antibody reactivity in systemic lupus erythematosus patients.

Antinuclear antibodies (ANA) are a hallmark of systemic lupus erythematosus (SLE) and one of its key diagnostic criteria. Recently, new technologies based on antibody binding to fluorescence beads (FB) have been widely employed for ANA screening. We conducted a formal study in 385 consecutive patients who underwent both traditional immunofluorescence (IF) and FB testing and evaluated each patient for the diagnosis of SLE. The distribution of ANA test results was significantly different (chi(2)=73.12; p<0.0001) due to a marked discordance of double-negative and double-positive results. The concordance of the FB-negative and IF-negative test results was 240/256 (95.6%), while the concordance of double-positive results was 54/129 (41.9%). The sensitivity of IF was markedly higher (48/53; 90.6%) than that of the FB (26/53; 49.1%; p<0.0001) for the diagnosis of SLE. IF had a lower specificity (76%) than FB (87%; p=0.0002). The present data show that the IF assay has superior sensitivity for detection of ANA and should continue to be used as the primary screening test for the diagnosis of SLE.