Anti-double stranded deoxyribonucleic acid antibodies testing - comparison between immunofluorescence assay and automated enzyme immunoassay: A single center experience

Abstract

Background Autoimmune rheumatic diseases are autoimmune disorders presented with joint and muscles manifestations. They are characterized by presence of antinuclear antibodies (ANA). ANA include autoantibodies to extractable nuclear antigens, autoantibodies to histones and deoxyribonucleic acid (DNA). Anti-double stranded DNA (dsDNA) antibodies are recognized as diagnostic markers of systemic lupus erythematosus (SLE) and as indicators of SLE disease activity, especially in lupus nephritis. The significance of anti-dsDNA in SLE diagnosis and in monitoring SLE disease activity has led to increase in this test laboratory requests as well as in the number of commercially available kits. Aim of the work This study aims to evaluate the performance of Alegria anti-dsDNA screen test method in the Laboratory of Clinical Immunology, Assiut University and to compare its results to the results obtained by immunofluorescence method. Materials and methods Evaluation of the performance of Alegria anti-dsDNA screen test as a qualitative test was evaluated through method comparison according to Clinical and Laboratory Standard Institute (CLSI) guidelines. Results obtained by Alegria anti-dsDNA screen kit were compared with that obtained by nDNA Fluoro-Kit indirect fluorescent antibody test. Manufacturer's recommended reference interval of Alegria anti-dsDNA screen was verified according to CLSI guideline. Result Alegria anti-dsDNA screen ELISA kit showed 94.4% positive agreement, 37% negative agreement and 65.7% overall agreement with nDNA Fluorokit. In the verification study of manufacturer's reference interval (negative <25 U/ml), 5/40 specimens (12.5%) from healthy subjects were positive which exceeds the acceptance criteria of 10%. ROC curve methodology was used to analyze results of both methods and cut off value was adjusted. With cut off adjustment, method specificity increased but sensitivity was decreased. Optimal cut off was determined to be 74U/ml with acceptable level of both sensitivity and specificity (72% and 74%, respectively). Conclusion Alegria anti-dsDNA screen method demonstrated good sensitivity and low specificity. With manufacturer's cut off adjustment, specificity was improved. Manufacturer's reference interval of Alegria anti-dsDNA screen was not verified. A new cut off value was suggested, for further validation in an independent study.