Concordance between tuberculin skin test and interferon-γ assay and interferon-γ response to mitogen in pediatric tuberculosis contacts.

There is paucity of data on the usefulness of Interferon (IFN)-γ release assays in the diagnosis of latent tuberculosis infection (LTBI) in children. The aim of this study was to evaluate the concordance between tuberculin skin test (TST) and QuantiFERON®-TB Gold in-tube (QFT-GIT) test, when used in contact screening to diagnose LTBI in asymptomatic children. We also aimed to determine if there is any correlation between age and the IFN-γ response to the mitogen. Children assessed at Leicester Royal Infirmary and Glenfield hospital (Leicester, United Kingdom) as part of tuberculosis contact screening were studied. Two hundred and eighty three children (mean [SD] age 5.3 [4.1] years, 148 males) underwent clinical examination, chest radiograph, TST, and QFT-GIT test. In this group, there was good agreement (κ = 0.70 [95%CI = 0.57-0.83], P < 0.0001) between TST and QFT-GIT. Of the 18 children in this group with an indeterminate QFT-GIT test result, all except one were < 5-years-old. To study the correlation between age and the IFN-γ response to the mitogen, results of 282 children who had QFT-GIT test as part of tuberculosis contact screening during the study period were analyzed. A significant correlation was observed between age and the IFN-γ response to the mitogen (r = 0.47, P < 0.001). Whilst our study re-emphasizes the good overall concordance between TST and QFT-GIT, the high rate of indeterminate results and the low IFN-γ response to the mitogen seen in young children raise some concerns about the performance of IGRAs in this group.