• Tuberculosis

The study reported by Lucas et al1 is a valuable addition to recent publications that have compared the performance of commercial interferon-γ release assays (IGRAs) with that of the tuberculin skin test (TST) for the diagnosis of latent tuberculosis infection (LTBI) in high-risk children.2 3 However, we believe that the principal conclusions are not supported by the data provided and that a more guarded interpretation is warranted.

In agreement with previous studies in children,3–5 Lucas et al found significant discordance between the results of IGRAs and TST. Specifically, of 420 T-SPOT.TB and 460 QuantiFERON-TB Gold I Tube (QFT-GIT) assays that were successfully completed, results were positive in 38 (9%) and 45 (10%) children, respectively. In contrast, of 304 children in whom the TST was read, the result was positive in 54 (18%). The authors contend that the overall low level of agreement between TST and IGRAs (κ =0.45–0.46) in their study ‘reflects the likely superior specificity of the IGRAs resulting from the use of antigens not found in either BCG or NTM’. However, the authors' own data suggest that previous BCG …