IFA is the standard ANA testing method because it is easy to perform, inexpensive, and offers high specificity and sensitivity. Also, it has the advantage that the patterns visualized under fluorescence microscope using this method can be correlated with certain autoimmune diseases. These patterns are a result of the adhesion of ANAs to nuclear antigenic structures—this is why they may be associated with certain autoantibodies and certain clinical conditions.
Although the IFA presents no organ specificity, it is an important step in the investigation and diagnosis of autoimmune diseases. ANAs can also be considered markers of evolution and prognosis, which is why the possibility of correlation between IF patterns and certain autoantibodies conveys a major advantage in clinical evaluation. For example, it has been observed that patients with juvenile idiopathic arthritis who test ANA positive present similar disease characteristics and more frequently develop iridocyclitis, compared with those who test ANA negative.
Positive results of ANA testing must be interpreted only in a clinical context because of the possibility of a positive test result in a healthy person, especially in elderly people or in pathological conditions other than autoimmune diseases. In the future it will be important to develop IF methods, to improve the accuracy of discrimination between healthy people who test ANA positive and patients with autoimmune disease.
ANAs, antinuclear antibodies; SLE, systemic lupus erythematosus; SS, scleroderma; SjS, Sjögren syndrome; MCTD, mixed connective tissue disease; PM, polymyositis; RA, rheumatoid arthritis; PBC, primary biliary cirrhosis; ENAs, extractable nuclear antigens; dsDNA, double-stranded DNA; Sm, Smith antigen; CTDs, connective tissue diseases; IFA, indirect immunofluorescence assay; ELISA, enzyme-linked immunosorbent assay; PML, promyelocytic leukemia protein; SS-CREST, calcinosis, Raynaud phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia; snoRNP, small nucleolar ribonucleoprotein; NORs, nucleolar organizing regions; RNAP I, RNA polymerase I.
Lab Med. 2018;49(3):e62-e73. © 2018 American Society for Clinical Pathology