Antinuclear antibodies: two-step detection strategy

In order to evaluate the performance of the chemiluminescent immunoassay (CLIA) in antinuclear antibodies (ANA) testing, using indirect fluorescent antibody (IFA) on HEp-2 cells as a standard, 209 samples were studied from September to October/2010. The tests were conducted according to the procedures recommended by the manufacturers of the reagents. The interpretation of the IFA results was done according to the Brazilian standards. The charts of patients showing different results between the two techniques were analyzed. The CLIA efficiency was 89%, with a sensitivity of 65%, and a specificity of 94.7%. Nine (4.3%) false-positive and 14 (6.7%) false-negative results were detected. Of these, 13 (93%) represented no risk for the diagnosis and therapeutic management of the patients. The CLIA methodology reduced the need for the IFA manual technique by 77% (160/209). The ANA screening test proved to be a fast and acceptable methodology in the studied population. We established the following criteria for the introduction of an automated ANA screening: (1) Positive results must be confirmed by IFA to characterize the pattern and titer of the antibody. (2) Negative results are issued with a notice to request a new test by IFA when the clinical suspicion of autoimmune disease persists.