Different strategies for latent TB assessment in patients undergoing anti-TNF treatment: an economic model

OBJECTIVES: Since treatment with biologics may reactivate latent TB, testing and prophylaxes before initiating therapy are mandatory. However, there is not a unique solution for the number and type of tests to be used for detecting the presence of TB, and for the definition of when prophylaxis should be prescribed. Which alternative should be preferred depends on the effectiveness of treatment and also on the cost associated. This methodological study aims to define a general economic model to assess different protocols for latent TB detection in patients undergoing anti-TNF treatment. METHODS: A decision tree approach has been designed for comparing alternative protocols in terms of (a) expected costs of different strategies for latent TB assessment in patients undergoing anti-TNF treatment; b) the economic convenience of the prophylaxis therapy in presence of a negative chest X-ray. Uncertainty is expressed by the probability of being positive and negative to the tests. In the NHS perspective the model considers: costs of tests; costs of TB onsets for rheumatologic patients who undergo biologics; costs of extending anti TB prophylaxis also to false negative patients; costs related to 1-month biologic therapy delay because of prophylaxis; costs for adverse events therapy and/or test related. Indirect costs are also considered in the broader societal perspective. RESULTS: Costs assessed are useful to choose the less costly alternatives. The comparison also considers the reduction of false negatives to the tests which do not follow prophylaxis while being affected by latent TB. CONCLUSIONS: The model, that can represent a useful tool both for clinical and health policy decision making, is a general one; it can be applied to any country by inserting the country specific epidemiological, clinical, and economical data, and to any anti-TNF drug, by using the specific biologic drug-related risk factor.