Repeat Interferon γ Release Assay Use in US Community Healthcare Organizations
Jeffrey I Campbell1, Meredith B Brooks2, Leonardo Martinez3
1Section of Pediatric Infectious Diseases, Department of Pediatrics, Boston Medical Center, Boston, Massachusetts, USA.
Background:
Interferon γ release assays (IGRAs) are the preferred test for tuberculosis infection in the United States. Their results 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 result 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 we estimated repeat IGRA overuse and underuse.
Results:
Among 65 728 individuals with a positive IGRA result, 8978 (13.7%) had ≥1 subsequent test. Of the 8174 second tests with full results available for analysis, 6176 (75.6%) remained positive, 1904 (23.3%) reverted to negative, and 94 (1.2%) were uninterpretable. Lower odds of reversion were associated with higher initial Antigen minus Nil (Ag-Nil) value (adjusted odds ratio, 0.38 [95% confidence interval, .32-.45] for Ag-Nil 0.70 to <1.00, and 0.06 [.05-.07] for Ag-Nil ≥1.00 vs 0.35 [vs Ag-Nil 0.35 to <0.70 IU/mL]), and birth in a country with versus birth in a country without elevated tuberculosis incidence (adjusted odds ratio, 0.59 [95% confidence interval, .52-.67]). 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 IGRA results 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.
