Discordance between tuberculin skin test and interferon-γ release assay in children younger than 5 years who have been vaccinated with bacillus Calmette-Guérin

Abstract

Background: Interferon-γ release assays (IGRAs) offer the possibility of improved detection of latent tuberculosis infection (LTBI). Objective: To analyze discordant tuberculin skin testing (TST) and IGRA results in ethnic Croatian children as old as 5 years for whom there is documented exposure to an adult with active tuberculosis (TB) and who have been vaccinated with Bacillus Calmette-Guérin. Methods: In specimens from our cohort individuals, we tested the performances of the QuantiFERON-TB Gold In-Tube (QFT-GIT) test and TST and analyzed discordant results. Results: At the TST cutoff value of 10 mm or greater, the estimated prevalence of M. tuberculosis infection was 18.1% (31/171) using TST and 15.2% (26/171) using QFT-GIT. The results of these 2 tests showed an overall concordance of 87.7%. There was no evidence that subjects' age correlated with discordant results. Conclusions: The reasons for discordant results in young children are still unclear, which highlights the importance of further longitudinal studies to better understand the interpretation and any possible clinical implications of the results of these tests.