P-787. Potential Impact of Repeating Unexpected Positive Interferon Gamma Release Assays

Abstract Background Interferon gamma release assays (IGRAs) are more specific for tuberculosis infection than the tuberculin skin test but also have higher test-retest variability. False positive tests may occur in low prevalence populations. As such, repeating unexpected positive tests (positive tests in patients without exposure risk) is recommended.Table:Initial and repeat IGRA results Methods We performed a retrospective electronic record review of all patients for whom a QuantiFERON (IGRA) was performed in Duke University Health System between 10/1/2014-5/3/2024. We examined patterns of repeat testing and ascertained the potential clinical impact of repeat testing. Results In total, 59,485 IGRAs were performed on 49,850 patients during the study period. 7,076 patients had repeat IGRA testing (median 2 IGRAs, range 2-9). Of these, 6137 had negative, 297 positive, and 642 indeterminate results on the first test. When repeat testing was performed, 743 (11%) patients had a different result on the second test (Table). Of patients with initial positive results, 104/297 (35%) had a negative result on the second test, which was performed a median of 110 days later (IQR 16-420 days). 86 patients had a negative first test but a positive second test; of these, 38 had a third test performed that was negative in 27 (71%) and positive in 11 (29%). Conclusion In a low-prevalence setting, repeating positive IGRA tests potentially avoided unnecessary preventive treatment in over a third of patients with an initial positive test and in two-thirds of patients with a prior negative test. Disclosures Nicholas A. Turner, MD, MHSc, PDI: Research contract|Purio Labs: Research contract