A COMPARATIVE STUDY OF ENZYME LINKED IMMUNOSORBENT ASSAY (ELISA) WITH IMMUNOFLUORESCENCE ASSAY (IFA) FOR THE DETECTION OF ANTI NUCLEAR ANTIBODIES

Abstract

Anti-nuclear antibody (ANA) testing is widely used as a screening test in Autoimmune diseases. The most commonly used method for ANA testing is ANA-immunofluorescence assay (ANA-IFA). This study compared the diagnostic performance of Enzyme linked immuno sorbent assay (ELISA) with IFA for the detection of ANA. 125 samples were tested which included 75 samples from patients with clinical suspicion of autoimmune diseases and 25 positive and negative controls. Of the 75 test samples, IFA was positive in 31 (41.3%), negative in 44 (58.6 %) cases. ELISA was positive in 20 ( 26.6 %), negative in 55 (73.3%) cases. 13 (17.3%) samples were positive by both methods. 37 (49.3%) samples tested negative  by both. 18 (24%) samples were IFA positive but ELISA negative. 7 samples (9.3%) were ELISA positive but IFA negative. Comparing with the gold standard IFA, the sensitivity of ELISA was 71.43% and the specificity was 86.84%. ANA by ELISA is less sensitive than IFA using the HEp 2 substrate. Positive and negative controls tested by both methods gave the expected results.