BACKGROUND: The new interferon-γ release assays (IGRAs) offer alternatives to the traditional tuberculin skin test (TST) for diagnosing latent tuberculosis infection (LTBI). Advantages include the fact that they require only one patient visit, do not boost responses in second tests, and are not affected by prior BCG vaccination, thus providing greater specificity. We compared the cost effectiveness of 3 strategies for detecting latent tuberculosis infection (LTBI) in new VA health care workers (HCWs): QuantiFERON®-TB Gold (QFT-G), QuantiFERON-TB® Gold In Tube (QFT-GIT), and TST.

METHODS: We constructed a Markov state transition decision analytic model, using the societal perspective and lifetime horizon, to compare the 3 strategies for hypothetical 35-year-old HCWs with or without prior BCG vaccination. Direct costs, costs of missed work time, and probabilities were based on manufacturers' data, national VA data, and the published literature. We calculated the incremental costs per quality-adjusted life year (QALY) gained for the three strategies, discounting future costs and QALYs at 3% per year. We performed sensitivity analyses, varying all of the input parameters over wide ranges.

RESULTS: The 2 IGRA strategies were both more effective and less costly than the TST strategy whether or not the HCW had been previously BCG vaccinated. For non-BCG-vaccinated HCWs, the incremental cost-effectiveness of QFT-G compared with QFT-GIT was $14,092/QALY. For BCG-vaccinated HCWs, the incremental cost-effectiveness of QFT-G was $103,047/QALY. There was no prevalence of LTBI at which TST became the most effective or least costly strategy for either cohort. Additional sensitivity analyses showed that if the sensitivity of QFT-GIT exceeded that of QFT-G, then QFT-GIT would be the most effective and least costly strategy.

CONCLUSIONS: QFT-G and QFT-GIT are clinically and economically worthwhile alternatives to TST and should be considered in screening non-BCG and BCG-vaccinated HCWs for LTBI. Although both IGRA strategies have similar costs and benefits in non-BCG-vaccinated HCWs, QFT-GIT may be preferred in BCG-vaccinated HCWs.