Interferon-gamma release assays for the detection of Mycobacterium tuberculosis infection in children with cancer.

SETTING The paediatric oncology unit at Tygerberg Children's Hospital, South Africa. OBJECTIVES To assess the use of the tuberculin skin test (TST) and two commercial interferon-gamma release assays (IGRAs) for the detection of Mycobacterium tuberculosis infection in children with cancer before initiating chemotherapy treatment. DESIGN Prospective hospital-based study, including children newly diagnosed with cancer; all underwent TST and IGRA testing. RESULTS Of the 34 children enrolled, seven (17.6%) tested positive with either test: TST (3/7, 8.8%), T-SPOT.TB (n = 6, 17.6%) and QuantiFERON-TB Gold In-Tube (QFT-G; n = 3, 8.8%). T-SPOT.TB assay results were negative in 17 (50.0%) and indeterminate in four (11.8%) children. Six T-SPOT.TB tests could not be completed due to low cell counts (<100,000 per well), and one clotted. QFT-G results were negative in 26 (76.5%) and indeterminate in five (14.7%). CONCLUSIONS TST and IGRAs were frequently discordant, with fewer positive results than expected. T-SPOT.TB produced more positive results, but inadequate cell counts were a particular problem. The sample size was too small to comment with confidence on test accuracy. All latent TB infection tests appear to perform sub-optimally in this group of children, and therefore none of them can be used in isolation to confirm or disprove TB infection.

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