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Tuesday, 19 April 2016 16:04

Paper 2016_04

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Prognostic value of interferon-γ release assays, a population-based study from a TB low-incidence country.

Hermansen TS, Lillebaek T, Langholz Kristensen K, Andersen PH, Ravn P.

Thorax.2016 Mar 30. pii: thoraxjnl-2015-208228. doi: 10.1136/thoraxjnl-2015-208228. [Epub ahead of print]






The ability of interferon-γ release assays to predict the development of TB has been investigated in many studies, but few cases develop TB during follow-up limiting the generalisation of results.


We assessed QuantiFERON-TB Gold In-Tube test (QFT) results from 15 980 Danish individuals and data on all TB cases in Denmark from 2005 to 2012 and determined the predictive value of the QFT for coprevalent TB (0-90 days after testing) and incident TB (>90 days).


Coprevalent TB was diagnosed in 10.7% (183/1703) and 0.3% (38/13 463) cases with a positive and negative QFT, respectively. For the QFT-positive cases, coprevalent TB was more frequent among persons <35 years compared with those >35  years (19.3% vs 7.2%, p<0.001). The cohort was followed-up for 52 807 person-years, median follow-up time was 3.36 years. For incident TB, the positive and negative predictive values (PPV and NPV) were 1.32% and 99.85%, respectively. Incidence rates (IR) for incident TB among QFT-positives and QFT-negatives were 383 per 105 and 45 per 105 person-years, respectively. Among cases with a positive QFT, IR for incident TB was associated with time interval since QFT (<2 years, p<0.001), but not with age (<35 years, p=0.087).


We confirmed a high NPV of the QFT and found positive QFT associated with a higher risk of subsequent incident TB. Overall, the PPV for incident cases was 1.32%, and development of incident TB was associated with time interval after the QFT, but not with age.

Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to



In this study by our TBnet member Pernille Ravn and colleagues, results from the QuantiFERON TB gold in tube test from whole Denmark were retrospectively collected from a total of 15980 persons along with information for potential progression towards tuberculosis. Indications for screening were mixed and mainly included contacts, patients prior to anti-TNF treatment and suspects for active tuberculosis. Main results are summarized in a slide set.

This is the largest country-wide analysis of IGRA tests and progression with important implications for low-prevalence countries. The number of coprevalent cases proved to be high emphasizing the value to identify TB cases during screening for LTBI. Finally, this study adds to the growing evidence that currently used IGRAs have a poor PPV for predicting progression towards tuberculosis (Chosen and summarized by Prof. Martina Sester).

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