Repeat Interferon Gamma Release Assay Use in US Community Healthcare Organizations

Abstract Background Interferon gamma release assays (IGRA) are the preferred test for TB infection in the US. IGRAs can fluctuate from positive to negative (reversion), but there is limited information about who does or should receive repeat testing in routine clinical care. Methods We performed a retrospective cohort study of all individuals with a positive IGRA in a US community health organization network (OCHIN). We characterized the frequency and predictors of repeat testing and reversion. We used published recommendations to classify repeat IGRAs as “likely”, “possibly”, and “probably not” indicated, and estimated IGRA over- and under-utilization. Results Among 65,728 individuals with a positive IGRA, 8,978 (13.7%) had >1 subsequent test. Of the 8,174 second tests with full results available for analysis, 6,176 (75.6%) remained positive, 1,904 (23.3%) reverted to negative, and 94 (1.2%) were uninterpretable. Higher initial Ag-Nil value (Ag-Nil 0.70-<1.00 aOR 0.38 [95%CI 0.32, 0.45] and Ag-Nil >1.00 aOR 0.06 [95%CI 0.05, 0.07], vs. Ag-Nil 0.35-<0.7), and birth in a country with elevated TB incidence (vs. birth in a country without elevated TB incidence, aOR 0.59 [95%CI 0.52, 0.67]) were associated with lower odds of reversion. Of all repeat tests, 40.0% were likely indicated, 9.0% were possibly indicated, and 51.0% were probably not indicated. Conclusions Approximately 1 in 7 individuals with positive IGRAs had repeat testing. Most repeat tests were probably not indicated according to our utilization classification, whereas nearly half of individuals without a repeat test may have benefited from one.