The clinical utility of a positive antinuclear antibody test result

Background: This retrospective study investigated the clinical utility of a positive antinuclear antibody (ANA) test performed outside of the rheumatology setting. Prior studies have investigated the frequency of ANA positivity within the general population. The purpose of this investigation was to evaluate the clinical utility of a positive ANA test result in a real-world setting by reviewing the final diagnoses of patients who were referred to a tertiary rheumatology clinic for evaluation of a positive ANA test result.

Methods: We reviewed the records of patients presenting to the authors between July 2007 and July 2009. Patients were included in the evaluation if they were referred for a positive ANA test result. All relevant descriptive and laboratory data were collated, as were the initial reasons for ordering ANA testing and the ultimate diagnoses reached. Positive predictive values for a "positive ANA test result" were calculated for all antinuclear antibody-associated rheumatic diseases and for lupus specifically.

Results: A total of 232 patients were referred for a positive ANA test result. The positive predictive value of a positive ANA test result in this cohort was 2.1% for lupus and 9.1% for any antinuclear antibody-associated rheumatic disease. No antinuclear antibody-associated rheumatic disease was identified in patients with an ANA<1:160. The most common reason for ordering ANA testing was widespread pain (54/232, 23.2%).

Conclusions: In this retrospective study, more than 90% of patients who were referred to a tertiary rheumatology clinic for a positive ANA test result had no evidence for an ANA-associated rheumatic disease. The poor predictive value of a positive ANA in this cohort was largely attributable to unnecessary testing in patients with low pretest probabilities for ANA-associated rheumatic disease.