Performances of anti-nuclear antibody testing by immunofluorescence assay (ANA-IFA) and enzyme immunoassay (ANA-EIA) were compared in relation to patient diagnosis. A total of 467 patient serum samples were tested by ANA-IFA (Kallestad; Sanofi) and ANA-EIA (RADIAS; Bio-Rad), and their age, sex, diagnosis, disease status, and medications were obtained through chart review. Reference ranges were established by testing 98 healthy blood donor samples. Eighty-six samples came from patients with diffuse connective tissue diseases, including systemic lupus erythematosus, discoid lupus erythematosus, or drug-induced lupus (n ‫؍‬ 71); systemic sclerosis, CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal motility abnormalities, sclerodactyly, and telangiectasia), or Raynaud's syndrome (n ‫؍‬ 8); Sjögren's syndrome (n ‫؍‬ 5); mixed connective tissue disease (n ‫؍‬ 5); and polymyositis or dermatomyositis (n ‫؍‬ 3). The sensitivity, specificity, positive predictive value, and negative predictive value for ANA-IFA were 87.2, 48.0, 29.1, and 93.9%, respectively, for the reference range of <1:160. For ANA-EIA, they were 90.7, 60.2, 35.8, and 96.4%, respectively, for the reference range of <0.9. ANA-EIA offers equivalent sensitivity and higher specificity compared to ANA-IFA. Anti-nuclear antibody (ANA) testing is widely used as a screening test in connective tissue diseases (CTD) such as systemic lupus erythematosus (SLE), scleroderma, CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal motility abnormalities, sclerodactyly, and telangiectasia), Sjögren's syndrome, mixed connective tissue disease (MCTD), polymyositis, and dermatomyositis. However, positive ANA results are seen in a significant proportion of the elderly population (6, 17, 18, 20) and sensitivity of ANA testing varies widely from one clinical disease to another. For example, ANA testing has been reported to be positive in Ͼ95% of patients with SLE but in only 10 to 50% of patients with dermatomyositis and polymyositis (20). The first description of ANA was made by Hargraves and colleagues in 1948 when they observed LE (lupus erythematosus) cells in the bone marrow of patients with SLE (4). Currently, the most commonly used method for ANA testing is ANA-immunofluorescence assay (ANA-IFA) in which slides prepared from human epithelioid cells (HEp-2 cells) as a substrate are incubated with diluted serum. The presence of autoantibodies is detected by fluorescent antiimmunoglobulin antibody, and characteristic morphologic patterns of fluorescent staining are observed. Certain ANA-IFA patterns are associated with the presence of autoantibodies to certain nuclear antigens which in turn are associated with certain clinical states (7, 13, 17, 20). For example, a diffuse or homogenous pattern is associated with such clinical states as SLE, rheumatoid arthritis, scleroderma, Sjögren's syndrome, and drug-induced lupus. The ANA-IFA is a subjective assay requiring skilled personnel and is a manual assay with a significant amount of hands-on time. Therefore, ...

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