Prospective Comparison of Two Brands of Tuberculin Skin Tests and Quantiferon-TB Gold in-tube Assay Performances for Tuberculosis Infection in Hospitalized Children

ABSTRACT Objective: The study compared two brands of tuberculin skin tests (TST): PPD RT 23, (SSI, Denmark) and PPD IC 65, (Cantacuzino Institute, Romania), 2 TU/ 0.1 ml each, with an interferon gamma release assay [IGRA], Quantiferon–TB Gold (QFT). Material and methods: QFT was performed on whole blood samples, before TSTs, on 60 children with tuberculosis (TB), BCG vaccinated, admitted in a paediatric pneumophtisiology hospital. The proportion of boys (51.6 %) and girls (48.3 %) was nearly equal, the mean age of subjects was 9.44 years (SD= 5.37 years; variance= 28.83). Results: With TST induration ≥ 10 mm considered as positive response, only 47.46 % of children classified positive with RT23 and 48.27 % with IC-65, were IFN-γ positive.We obtained a very good agreement between the two tuberculins (59/60 for RT 23 and 58/60 for IC 65), while for QFT, which confirmed as positives only 27/60, i.e. 45 % (18/60 were indetermined, 15/60 were negatives). Conclusions: The tests did not agree on positive results, showing a low redundancy between in vitro and in vivo measurements, suggesting that independent aspects of anti-mycobacterial immunity are being measured by these tests.The specificities of the assays could not been calculated since all the children had TB, confirmed by bacteriological and/ or clinical and radiological data. Further comparison of TST and QFT, may determine whether such discordance reflect a higher specificity of QFT. Meantime, we are trying to obtain a recombinant PPD, using a cocktail of specific M. tuberculosis (M.tb) antigens, in order to eliminate any interference with BCG in skin test reactions.