Interferon-γ release assays versus tuberculin skin test for targeting people for tuberculosis preventive treatment: an evidence-based review

Objectives: To assess whether Interferon-γ release assays (IGRAs) reduce the number of people considered for tuberculosis (TB) preventive treatment without increasing subsequent active disease.

Methods: Longitudinal studies with both tuberculin skin test (TST) and IGRAs were identified through a PubMed search. Reductions in diagnosis of TB infection and increases in incident TB in people considered not infected, using IGRAs either instead of TST or as a confirmatory test (two-step approach), were assessed.

Results: In comparison with TST alone, the pooled reductions in diagnosis of TB infection obtained with IGRAs were 16.7% and 5.8% at 5 and 10 mm cut-offs respectively, and 24.5% and 12.4% at 5 and 10 mm respectively with the two-step approach. Compared with TST alone, incident TB among people considered not infected increased with the two-step approach (0.94% with T-SPOT(®).TB and 1.1% with QuantiFERON(®)-TB Gold In-Tube) in one of seven studies in high-income countries. In middle- and low-income countries, two of four studies presented increases (0.08 and 0.03 per 100 patient-years respectively) with the two-step approach.

Conclusions: In high-income countries, the use of IGRAs, either instead of TST or as confirmatory test reduces the number of people considered for preventive treatment, without a significant risk of subsequent active disease.