Screening of healthcare workers for tuberculosis: development and validation of a new health economic model to inform practice

BACKGROUND: Methods for determining cost-effectiveness of different treatments are well established, unlike appraisal of non-drug interventions, including novel diagnostics and biomarkers. OBJECTIVE: The authors develop and validate a new health economic model by comparing cost-effectiveness of tuberculin skin test (TST); blood test, interferon-gamma release assay (IGRA) and TST followed by IGRA in conditional sequence, in screening healthcare workers for latent or active tuberculosis (TB). DESIGN: The authors focus on healthy life years gained as the benefit metric, rather than quality-adjusted life years given limited data to estimate quality adjustments of life years with TB and complications of treatment, like hepatitis. Healthy life years gained refer to the number of TB or hepatitis cases avoided and the increase in life expectancy. The authors incorporate disease and test parameters informed by systematic meta-analyses and clinical practice. Health and economic outcomes of each strategy are modelled as a decision tree in Markov chains, representing different health states informed by epidemiology. Cost and effectiveness values are generated as the individual is cycled through 20 years of the model. Key parameters undergo one-way and Monte Carlo probabilistic sensitivity analyses. SETTING: Screening healthcare workers in secondary and tertiary care. RESULTS: IGRA is the most effective strategy, with incremental costs per healthy life year gained of £10 614–£20 929, base case, £8021–£18 348, market costs TST £45, IGRA £90, IGRA specificities of 99%–97%; mean (5%, 95%), £12 060 (£4137–£38 418) by Monte Carlo analysis. CONCLUSIONS: Incremental costs per healthy life year gained, a conservative estimate of benefit, are comparable to the £20 000–£30 000 NICE band for IGRA alone, across wide differences in disease and test parameters. Health gains justify IGRA costs, even if IGRA tests cost three times TST. This health economic model offers a powerful tool for appraising non-drug interventions in the market and under development.