Magnitude of Interferon Gamma Release Assay Responses in Chi
This study assessed the association between quantitative interferon gamma (IFN) gamma response and degree of Mycobacterium tuberculosis exposure, infection and tuberculosis (TB) disease status in children.

Cross-sectional analysis of children exposed to an adult with bacteriologically confirmed TB was completed. IFN gamma values were reported as concentrations and spot forming units for the QuantiFERON-TB Gold In-Tube (QFT-GIT) and T-SPOT.TB, respectively. Random-effects linear regression was used to investigate the relation between the M. tuberculosis contact score, clinical phenotype (TB diseased, infected, uninfected) and IFNgamma?response as outcome, adjusted for relevant covariates.

Data from 669 children (median age, 63 months; interquartile range, 33–108 months) was analyzed.

--A 1-unit increase in M. tuberculosis contact score was associated with an increase of IFNgamma 0.60 international unit/mL, and IFN gamma spot forming unit 2 counts.

--IFNgamma response was significantly lower among children with M. tuberculosis infection compared with children with TB disease (beta = –1.42) for the QFT-GIT, but not for the T-SPOT.TB.

--This association was strongest among children 2–5 years and absent if less than 2 years.

Finally, IFN gamma response was connected with recent exposure to M. tuberculosis evaluated by QFT-GIT and T-SPOT.TB and was correlated with clinically relevant TB phenotype by QFT-GIT. The size of the gamma reaction. In addition to evaluating the probability of M. tuberculosis infection, IFN gamma readings can also help diagnose children with TB.