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Thorax. 2018 Apr 5. pii: thoraxjnl-2017-211147. doi: 10.1136/thoraxjnl-2017-211147. [Epub ahead of print]

Stratification by interferon-γ release assay level predicts risk of incident TB.

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Department of Vaccine Preventable Diseases, Norwegian Institute of Public Health, Oslo, Norway.
Department of Infectious Disease Epidemiology and Modelling, Norwegian Institute of Public Health, Oslo, Norway.
Department of Medical Microbiology, Stavanger University Hospital, Stavanger, Norway.
Department of Microbiology, Haukeland University Hospital, Bergen, Norway.
Department of Clinical Science, University of Bergen, Bergen, Norway.
Department of Infectious Disease Immunology, Norwegian Institute of Public Health, Oslo, Norway.
Department of Tuberculosis, Blood Borne and Sexually Transmitted Infections, Norwegian Institute for Public Health, Oslo, Norway.
Department of Pharmacoepidemiology, Norwegian Institute of Public Health, Oslo, Norway.
Department of Infectious Diseases, Oslo University Hospital, Oslo, Norway.
Department of Acute Medicine, Oslo University Hospital, Oslo, Norway.
Department of Microbiology, Oslo University Hospital, Oslo, Norway.
Department of Microbiology and Infection control, Akershus University Hospital, Lørenskog, Norway.
Department of Microbiology and Infection Control, University Hospital of North Norway, Tromsø, Norway.
Research Group for Host-Microbe Interaction, Faculty of Health Sciences, UiT-The Arctic University of Norway, Tromso, Norway.
Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology, Trondheim, Norway.
Department of Medical Microbiology, St Olavs University Hospital, Trondheim, Norway.
Faculty of Medicine, Institute of Clinical Medicine, University of Oslo, Oslo, Norway.



Targeted testing and treatment of latent TB infection (LTBI) are priorities on the global health agenda, but LTBI management remains challenging. We aimed to evaluate 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 in a low TB incidence setting.


In this large population-based prospective cohort, we 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) to assess the prognostic value of QFT for incident TB. Participants were followed until 30 June 2016. We used restricted cubic splines to model non-linear relationships between IFN-γ levels and TB, and applied these findings to a competing risk model.


The prospective analyses included 50 389 QFT results from 44 875 individuals, of whom 257 developed TB. Overall, 22% (n=9878) of QFT results were positive. TB risk increased with the IFN-γ level until a plateau level, above which further increase was not associated with additional prognostic information. 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).


Consistently, QFT demonstrates increased risk of incident TB with rising IFN-γ concentrations, indicating that IFN-γ levels may be used to guide targeted treatment of LTBI.


interferon-gamma release assay; latent tuberculosis; quantiFERON TB-Gold; tuberculosis

Conflict of interest statement

Competing interests: None declared.

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