The use of decision-analytical modelling in economic evaluation of patch testing in allergic contact dermatitis

Objective: The objective of this observational prospective study was to demonstrate the cost effectiveness of patch testing in patients suspected of allergic contact dermatitis (ACD) and to determine the order in which different severity groups rank in terms of cost effectiveness. Design and Setting: This observational study was conducted on 567 patients from 10 investigator sites in the US over a period of 1 year. All patients with a suspicion of contact allergy who exhibited at least moderate disease activity were included in the study and were stratified according to disease severity and whether or not they were patch tested. In each severity category, the cost effectiveness of patch testing was evaluated. Patients who were ruled out for contact allergy (without the use of patch test) by the first 6 months after admission were excluded. A validated dermatology-specific quality of life (DSQL) instrument was administered to all patients at the start of the study, and at 6 and 12 months thereafter. The cost-effectiveness analysis is demonstrated using a decision-analytical model. Costs included office visits and prescription costs without generic substitution. The cost of patch testing was not included due to the large variation in price among commercially available products. Main Outcome Measures and Results: Patch testing was performed on 22% of patients with mild disease. 41% of patients with moderate disease and 50% of those with severe disease. There was a significant difference between the patch-tested and non-patch-tested groups in terms of the time to obtain a confirmed diagnosis (medians = 8 and 175 days, respectively) and a significant difference in the ratio of patients who had a confirmed diagnosis (88 and 69%, respectively). As a result of changes made in their lifestyle, 66% of patients in the patch-tested group and 51% in the non-patch-tested group reported 75% or more improvement in their disease symptoms after 6 months. Early confirmation of diagnosis helped reduce the prediagnosis cost of treatment which was mostly based on preliminary diagnosis. The greatest quality-of-life (QOL) benefits from patch testing relative to nonpatch testing occurred in patients with recurrent/chronic ACD. Conclusions: Patch testing is most cost effective and reduces the cost of therapy in patients with severe ACD. Greater improvements in quality of life were seen in patients with recurrent/chronic ACD who were patch tested than patients who were not patch tested within the same group. Results were not sensitive to changes due to the addition of indirect costs or costs using generic substitution.