Methods. A long-term cost-effectiveness analysis of a multidisciplinary primary care diabetes management program was conducted for the province of Ontario. A retrospective chart review of all 404 patients with diabetes enrolled in the program was performed to collect individual patient-level clinical data. In order to estimate the costs for diabetes related complications, all incident cases (>= 35 years of age) in Ontario between the years 1994-2004 were identified (N=610,852) and matched to a non-diabetes cohort (N=1.22 million). Further subsets include all diabetic and non-diabetic patients who experienced a complication (i.e., amputation, angina, blindness, heart failure, myocardial infarction, nephropathy, and stroke). For all cohorts, the annual total cost includes hospitalization, outpatient services, public drug coverage, emergency room visits and home care services for up to 11 years of follow-up. These data were used as inputs in the Ontario Diabetes Economic Model in order to conduct a cost-effectiveness analysis. Incremental costs and incremental cost-effectiveness ratios were compared between using costs of complications derived from non-diabetic patients versus costs of complications derived from diabetic patients.

Results. When using non-diabetic population data, the costs of complications for the interventional group are $45,538, and for the control group are $45,728 for a difference of -$190. When the diabetic population costs are applied, the complication costs for the intervention group rise to $70,114, and for the control group rise to $70,521 for a difference in the cost of complications of -$407. This 54% rise in costs translates into doubling of the overall incremental cost and a 50% reduction of the incremental cost-effectiveness ratio from $3,971 to $1,979 per QALY.

Conclusions. The cost of a disease specific complication is higher than the cost of that same complication for the general population. By not considering this excess cost within disease specific costs of complications, there may be systematic bias in estimating incremental cost and the incremental cost effectiveness ratio.