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

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). 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. 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). 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.