No abstract

The purpose of this study was to analyze antinuclear antibody (ANA) screening by enzyme-linked immunosorbent assay (ELISA) followed by indirect fluorescent antibody (IFA) testing to confirm and characterize the pattern and titer of the antibody. We evaluated 4 ANA ELISAs and 1 HEp-2 IFA substrate in 224 clinically defined serum samples consisting of 30 from systemic lupus erythematosus (SLE) cases, 94 from rheumatoid arthritis cases, and 100 from healthy donors plus 495 serum samples submitted for routine ANA testing and 12 reference serum samples distributed by the Centers for Disease Control and Prevention. IFA tests were read independently by 2 certified medical technologists. ELISA sensitivities ranged from 90% to 97% compared with 80% by IFA in the SLE serum samples. The ELISAs had specificities of 36% to 94%, whereas the IFA had 99% specificity. Overall, ELISAs for ANA assays demonstrated better sensitivity and good specificity, suggesting ELISA is a more cost-effective alternative to IFA testing for initial ANA screening. Samples positive by ANA ELISA should be tested on HEp-2 to determine the titer and pattern.

We evaluated 5 commercially available HEp-2 antinuclear antibody (ANA) indirect fluorescent antibody (IFA) assays using patient serum samples from 45 patients with rheumatoid arthritis, 50 with systemic lupus erythematosus (SLE), 35 with scleroderma, 20 with Sjögren syndrome, 10 with polymyositis, and 100 healthy control subjects. In addition, 12 defined serum samples from the Centers for Disease Control and Prevention and 100 patient serum samples sent to ARUP Laboratories (Salt Lake City, UT) for ANA IFA testing were also examined (n = 372). Standardization among the HEp-2 IFA assays occurred when they exhibited the same titer ± 1 doubling dilution. Agreement of the 5 assays was 78%. Within the specific groups of serum samples, agreement ranged from 44% in scleroderma serum samples to 93% in healthy control subjects, with 72% agreement in the SLE group. Variations in slide and substrate quality were also noted (ie, clarity, consistency of fluorescence, cell size, number and quality of mitotic cells). Along with subjectivity of interpretation, HEp-2 IFA assays are also vulnerable to standardization issues similar to other methods for ANA screening.