Background Anti-nuclear antibodies (ANA) are common in systemic rheumatic diseases, non-rheumatic autoimmune diseases and the general population. In clinical practice, testing for ANA can inform further clinical diagnoses even in the absence of symptoms to suggest SLE or connective tissue disease. This study was undertaken to evaluate whether ANA testing result informed clinical diagnosis.

Methods The UT Southwestern Medical Center IRB approved this study. Data were obtained by SQL queries of the Epic electronic health record. The study population included all patients for whom an ANA was ordered at UT Southwestern Medical Center January 1, 2010 to June 30, 2017. The titer and pattern of the ANA as well as the results of ENA or anti-dsDNA testing were obtained. Patient characteristics included age and sex. Encounter characteristics included the date of testing, frequency of testing, primary encounter diagnosis, and provider specialty.

Results During the study period, a total of 33,270 ANA were ordered in 28,659 unique patients. Twenty two thousand, five hundred and twenty nine of the ANAs were tested in outpatients, representing 0.7% of all office visits during this time. 3,505 patients (11.9%) had ANA tested multiple times (range: 2-25 times). In 31% of the patients having multiple ANA, the result was repeatedly negative; 41% stayed repeatedly positive; 16% of patients had an initial negative ANA and a subsequent positive; 12% had an initial positive and a subsequent negative ANA.

Forty-nine percent of the ANA tests were positive at a titer of 1:80 or greater; slightly more women (51%) had a positive ANA (≥1:80) than did men (43%). Fifty-four and a half percent of the positive ANA in women were 1:320 or greater vs. 41.6% in men (p<0.0001. In this cohort, 143 patients who originally had a non-autoimmune disease listed as the reason for getting the ANA and who saw the same provider within 10-14 months and were subsequently given an autoimmune diagnosis.

Conclusions ANA testing in the inpatient and outpatient setting is common. Diagnoses precipitating testing are most often non-rheumatic conditions. A positive ANA result changed the clinical diagnosis in a small percentage of patients.