Cost-effectiveness of risk-stratified blood-test monitoring strategies for adults with inflammatory conditions

Objectives To assess the cost-effectiveness of extending the interval between monitoring blood-tests beyond three monthly intervals during established treatment of adults prescribed low-dose weekly methotrexate (≤ 25 mg/week), leflunomide, or sulfasalazine. Methods Published prognostic models that estimated the risk of stopping treatment due to abnormal blood test results during five years of established treatment were incorporated into a cost-effectiveness model. The consequences of having an extended monitoring period and delay in stopping treatment was estimated by clinicians as the probability of someone having one of the 11 adverse events (AEs) that could be avoided with monitoring. The clinicians erred towards over-estimating the risks. The costs and quality-adjusted life year loss of the AEs were sourced from recent National Institute of Health and Care Excellence appraisals or from targeted searches. Incremental net monetary benefit (iNMB) of six, 12, and 24 monthly monitoring, compared with three monthly monitoring was calculated for each drug conditional on risk decile. Results Our analyses show that extending the duration between monitoring appointments is cost-effective in all scenarios, even in a pessimistic analysis, where the risks of all AEs were tripled, and the costs of some AEs were increased. In the base case, biennial monitoring was often most cost-effective although the iNMB between annual and biennial monitoring was often small. Conclusion Extending the interval between monitoring blood-tests appears to be cost-effective with annual monitoring producing consistently good results regardless of assumptions related to risks of AEs, risk decile, or treatment.