Comparison of enzyme linked immunosorbant assaay (ELISA) with indirect immunofluorescence for detection of anti-nuclear antibody

Background: Detection of antinuclear antibody (ANA) is used as one of the diagnostic criteria for autoimmune rheumatic diseases (ARD). Both indirect immunofluorescence (IIF) and enzyme linked immunosorbant assay (ELISA) methods are used for this purpose. However, there are lack of data comparing these two tests from India. Methods: We prospectively studed 294 patients clinically suspected to be having ARD between April 2012 and September 2013. They were tested for ANA by IIF and ELISA methods. Representative samples positive by both the tests were processed again by a line immunoassay test to detect the specific antinuclear antibodies. Considering the IIF results as the ‘gold standard’, the utility of ELISA for ANA detection was analyzed. Results: Of the 294 samples processed, 181 (61.5%) were from female patients. By IIF 30% of samples in males and 40.3% sample in females tested positive. We found ELISA to have a poor sensitivity (45.8%) but good specificity (99.5%). The positive predictive value for ELISA were 98% and negative predictive value 76.2% respectively. Forty four samples positive by both IIF and ELISA were tested by Western blot to detect individual autoantibodies. Of these, only 24 samples showed the presence of one or more bands, while the remaining 20 (45.4%) were negative by line immunoassay. In our study anti-nuclear ribonucleoprotein/Smith was the most common ANA detected. Conclusions: The poor sensitivity raises concerns regarding the practice of initial screening for ANA by ELISA.