ANTINUCLEAR ANTIBODY TESTING - A STUDY OF CLINICAL UTILITY

Objective: To determine the clinical utility of the antinuclear antibo dy (ANA) test as ordered in a large teaching hospital. Methods: Retros pective chart review in a 400-bed teaching hospital that provides care for hospital-based and community-based practices. Patients: A consecu tive sample of 1010 patients (including inpatients and outpatients) fo r whom ANA testing was ordered over 10 months; all patients with posit ive ANA test results and an equal number of randomly selected patients with negative test results were included. Clinical utility of the ANA in the identification of rheumatic disease was determined by its esti mated sensitivity, specificity, and positive and negative predictive v alues. Results: Of 1010 ANA test results reviewed, 153 were positive. The group with positive ANA test results included more patients aged 6 5 years or older than the group with negative ANA test results (30% vs 15%, P<.003). The diagnosis of systemic lupus erythematosus (SLE) was established in 17 patients, all of whom had positive ANA test results . Other rheumatic diseases were found in an additional 22 patients. Th e estimated sensitivity and specificity of the ANA test for SLE were 1 00% and 86%, respectively. For other rheumatic diseases, sensitivity a nd specificity were 42% and 85%, respectively. The positive predictive value of the ANA test was 11% for SLE and 11% for other rheumatic dis eases. Specificity and positive predictive value for ANA testing in th e elderly patients were lower than among younger patients. Conclusions : The sensitivity of the ANA test for SLE was high, but overall the po sitive predictive value was low for SLE or other rheumatic diseases. S ensitivity was low for ANA testing among patients with non-SLE rheumat ic disease. More selective test ordering might improve the clinical ut ility of this test. Clinicians ordering the ANA test should be aware o f the test's low-positive predictive value in settings with a low prev alence of rheumatic disease, particularly among older patients.