Winje BA, et al. - In a low TB incidence setting, researchers assessed the prognostic value of the QuantiFERON TB-Gold (QFT) test for incident TB, focusing on the interferon (IFN)-γ level, when applied in routine practice. Increased risk of incident TB, with rising IFN-γ concentrations, were consistently shown by QFT. IFN-γ levels may be used to guide targeted treatment of latent TB infection.

Methods

• Researchers, in this large population-based prospective cohort, linked QFT results in Norway (1 January 2009–30 June 2014) with national registry data (Norwegian Surveillance System for Infectious Diseases, Norwegian Prescription Database, Norwegian Patient Registry and Statistics Norway).
• Until 30 June 2016, follow-up was performed.
• Using restricted cubic splines, non-linear links between IFN-γ levels and TB were modeled, and these findings were applied to a competing risk model.

Results

• In prospective analyses, 50,389 QFT results from 44,875 individuals were included, of whom 257 developed TB.
• Data showed that 22% (n=9878) of QFT results were positive.
• Until a plateau level, a rise in the TB risk was seen with the IFN-γ level, above which further increase was not related to additional prognostic information.
• Researchers found that the HRs for TB were 8.8 (95% CI 4.7 to 16.5), 19.2 (95% CI 11.6 to 31.6) and 31.3 (95% CI 19.8 to 49.5) times higher with IFN-γ levels of 0.35 to <1.00, 1.00 to <4.00 and >4.00 IU/mL, respectively, compared with negative tests (<0.35 IU/mL).