High Rates of Indeterminate TB Tests Among Hospitalized Patients: Can We Optimize Use of Gamma Interferon Release Assays in Tuberculosis?

In the United States, high concern for iatrogenic reactivation to tuberculosis (TB) disease secondary to prescribed immunosuppression has resulted in increased use of the QuantiFERON-TB Gold In-Tube test (QFT-GIT) to screen for Mycobacterium tuberculosis (Mtb) infection. The aim of our study was to determine indications for QFT-GIT testing and risk factors for indeterminate QFT-GIT results. We retrospectively identified patients with QFT-GIT testing over a six-month period in a tertiary care academic health care system and performed a record review. Inpatients were 11 times more likely to have an indeterminate QFT-GIT result than outpatients (95% CI 7.6-16.2). 61.5% inpatient QFT-GITs were ordered during workup of active TB. Providers treating exogenously or endogenously immunosuppressed patients ordered the most QFT-GITs. We highlight the significant limitations of TB screening tests in the inpatient setting and the need to test earlier in those requiring immunosuppressive therapy to avoid indeterminate results.