Comparison of a semiautomated fluorescent immunoassay system and indirect immunofluorescence for detection of antinuclear antibodies in human serum.

A semiautomated fluorescent immunoassay system (FIAX) for detecting anti-nuclear antibodies (ANAs) in human serum was compared with conventional indirect immunofluorescence using microscope slides (Meloy Laboratories) coated with mouse fibroblasts. The FIAX system uses quantitative indirect immunofluorescence to measure the specific binding of ANA to a sampler coated with human epithelial cells. A total of 101 serum samples were examined for the presence of ANAs by employing both methods. At an initial 1:10 screening dilution, 23 samples were negative for ANAs by the slide method, whereas 21 samples were negative with the FIAX system. Using 2+, 3+, and 4+ subjective brightness, 68 (100%) samples were positive by the slide method, whereas 67 (98.5%) were positive with the FIAX system. ANA-positive samples were diluted twofold from 1:10 to 1:640, and positive titers were determined by both methods. Sixty (77%) of 78 positive samples titrated by FIAX came within +/-1 dilution of the titers determined by the slide method, and 75 (96%) of the samples fell within +/-2 dilutions. Results indicate good correlation between the FIAX system and indirect immunofluorescence for the detection of ANAs in human serum. The FIAX system has the advantage of speed, reproducibility, and the elimination of subjective microscopic assessment of ANA titers.