Interferon gamma inducible protein-10 in the diagnosis of paediatric tuberculosis infection in a low TB incidence country.

Objective: To assess interferon-gamma inducible protein 10 (IP-10) as a diagnostic marker for tuberculous infection in children, particularly in relation to its differential diagnostic performance in young children.
Design and Results: A case-control study was conducted among 161 children and adolescents (mean age 6.3 years ± standard deviation 1.7; males n = 79, 49%). Fifty-four (33.5%) had active TB, 53 (33%) had latent tuberculous infection (LTBI), and 54 (33.5%) were non-LTBI controls. Unstimulated IP-10 levels did not differ between groups (P > 0.05 for all comparisons). TB-specific antigen stimulated IP-10 levels were more profoundly increased in infected groups than in controls (P < 0.001 for all comparisons). None of the IP-10-based diagnostic indexes demonstrated the ability to discriminate active disease from LTBI. A value of IP-10 ⩾ 1222 pg/ml had 83.3% sensitivity, 79.6% specificity, 80.4% positive predictive value and 82.7% negative predictive value for the diagnosis of LTBI. IP-10 based indexes demonstrated a trend towards better performance in the population group aged <5 years.
Conclusion: The IP-10 assay could be useful in improving the diagnosis of LTBI in patients aged <5 years in combination with existing interferon-gamma release assays.