Background: Interferon-γ release assays (IGRAs) for TB have the potential to replace the tuberculin skin test (TST) in screening for latent tuberculosis infection (LTBI). The higher per-test cost of IGRAs may be compensated for by lower post-screening costs (medical attention, chest x-rays and chemoprevention), given the higher specificity of the new tests as compared to that of the conventional TST. We conducted a systematic review of all publications that have addressed the cost or cost-effectiveness of IGRAs. The objective of this report was to undertake a structured review and critical appraisal of the methods used for the model-based cost-effectiveness analysis of TB screening programmes.
Methods: Using Medline and Embase, 75 publications that contained the terms "IGRA", "tuberculosis" and "cost" were identified. Of these, 13 were original studies on the costs or cost-effectiveness of IGRAs.
Results: The 13 relevant studies come from five low-to-medium TB-incidence countries. Five studies took only the costs of screening into consideration, while eight studies analysed the cost-effectiveness of different screening strategies. Screening was performed in high-risk groups: close contacts, immigrants from high-incidence countries and healthcare workers. Two studies used the T-SPOT.TB as an IGRA and the other studies used the QuantiFERON-TB Gold and/or Gold In-Tube test. All 13 studies observed a decrease in costs when the IGRAs were used. Six studies compared the use of an IGRA as a test to confirm a positive TST (TST/IGRA strategy) to the use of an IGRA-only strategy. In four of these studies, the two-step strategy and in two the IGRA-only strategy was more cost-effective. Assumptions about TST specificity and progression risk after a positive test had the greatest influence on determining which IGRA strategy was more cost-effective.
Conclusion: The available studies on cost-effectiveness provide strong evidence in support of the use of IGRAs in screening risk groups such as HCWs, immigrants from high-incidence countries and close contacts. So far, only two studies provide evidence that the IGRA-only screening strategy is more cost-effective.