Background/Purpose: Reducing unnecessary laboratory investigations is a health economic priority. Anti-nuclear antibody (ANA) testing is performed as part of the diagnostic work up for autoimmune disease, or in patients with inflammatory or musculoskeletal symptoms. The value of serial ANA testing is unclear, but anecdotal evidence suggests it is frequent. We sought to evaluate the utility of repeated ANA testing in a large tertiary healthcare network, to determine the evidence base for decision support actions.

Methods: The primary endpoint was whether a longitudinal change in ANA resulted in new ANA associated diagnoses. Secondary endpoints included calculation of the total cost associated with repeated testing and the examination of baseline ANA testing behaviours. We retrospectively analysed data from a multi-centre tertiary health network across a 7-year period (March 2011 to July 2018). ANA and other autoimmune test results were obtained from the hospital systems. The laboratory positive ANA cut off of 1:160 was used. Clinical information was sourced from medical records on all patients who had a change in ANA result from negative to positive on repeat testing. The cost of repeated ANA testing was calculated based on the baseline cost to the payer. Descriptive statistics were performed using Stata version 15.

Results: A total of 36,715 ANA tests (excluding 980 cancelled same-day requests) were performed in 28,840 patients. Of these, 14,058 (38.3%) were positive, with females accounting for 9,265 (65.9%, p< 0.001). The most frequent ANA patterns were homogenous (47.4%) and nucleolar (23.3%). The distribution of ANA titres was: 1:160 (41.4%), 1:320 (15.3%), 1:640 (13.1%) and 1:1280 (29.2%). 7,875 (21.4%) tests were repeat tests in 4,887 patients, with test frequency in an individual patient ranging from 2-45. Of repeated tests, 79% of results remained the same, while 541 (11.1%) results changed from negative to positive. In the 501 of these in whom medical records were available, a change to positive ANA was associated with a new ANA-associated diagnosis in only 7 cases (2 SLE, 1 scleroderma, 2 undifferentiated connective tissue disease and 2 autoimmune hepatitis), resulting in a positive predictive value of 0.014. When comparing patients with a new diagnosis to those with no new diagnosis, there was no difference between ANA titre, pattern, age, time interval between negative and positive ANA, location or ordering clinician. The direct total cost to the payer of all ANA testing was USD$624,691, of which repeat testing contributed USD$133,990.

Conclusion: Repeat ANA testing was frequent. After a negative result, repeat ANA testing has limited utility in the diagnosis of ANA-associated conditions with a very low positive predictive value, and was associated with excess cost. Clinical alert systems to reduce unnecessary repeat ANA testing may result in significant direct cost savings.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/ana-lysis-utility-of-repeated-antinuclear-antibody-testing-in-a-single-center/