The Utility of Interferon-γ Release Assays in the Diagnosis of Tuberculosis in Patients With Cancer.

Background: Patients with cancer are at elevated risk for tuberculosis (TB) reactivation. Diagnosis of latent TB infection and TB disease remains challenging in this patient population despite the advent of interferon-γ release assays (IGRA).

Methods: We retrospectively reviewed medical records of all patients with cancer who had IGRA testing (QuantiFERON-TB [QFT-TB] or T-SPOT.TB) at a major cancer center in the United States from June 2010 to July 2017. The results were analyzed with respect to the likelihood of latent TB infection and TB disease.

Results: A total of 1299 patients were included with 1599 tests performed: 586 QFT-TB and 1013 T-SPOT.TB. Forty-nine (4%) patients were diagnosed with latent TB, and four (1%) with TB disease. T-SPOT.TB was more likely to yield an actionable result (positive or negative) than QFT-TB (89% vs. 65%, p < 0.001). The rate of indeterminate results for QFT-TB was higher than the rate of invalid results for T-SPOT.TB (35% and 10%, respectively, p < 0.001). On multivariate analysis, independent predictors of an invalid T-SPOT.TB included prior receipt of alemtuzumab, lower hemoglobin, absolute lymphocyte count, or serum albumin (p < 0.05 each), whereas the independent predictors of an indeterminate QFT-TB were female gender, prior receipt of systemic corticosteroids, and lower hemoglobin, or serum albumin or higher absolute neutrophil count (p < 0.05 each).

Conclusions: T-SPOT.TB yielded more actionable results than QFT-TB in patients with cancer. T-SPOT.TB might be a better IGRA for screening for latent TB infection in patients with cancer, although a direct comparison would be needed to definitively determine this.