As implemented in the DPP and from a payer perspective, the lifestyle and metformin interventions cost $15,700 and $31,300, respectively, per case of diabetes delayed or prevented and $31,500 and $99,600 per QALY gained. From a societal perspective, the lifestyle and metformin interventions cost $24,400 and $34,500, respectively, per case of diabetes delayed or prevented and $51,600 and $99,200, respectively, per QALY gained. The lifestyle intervention was more cost-effective than the metformin intervention. Thus, in economic terms, the metformin intervention was dominated by the lifestyle intervention and should not be adopted if only cost-effectiveness is considered. To the extent that treatment availability, health insurance coverage, and patient and provider preferences drive clinical decision making, the metformin intervention may still be a worthwhile intervention for delaying or preventing type 2 diabetes.
Earlier research has demonstrated the effectiveness of group behavioral interventions relative to individual behavioral interventions (15
). If the lifestyle intervention were implemented in a group of 10 participants, the cost per case of diabetes prevented during the trial and the cost per QALY gained would decrease by >70% from a health system perspective and by >40% from a societal perspective. Similarly, if the metformin intervention could be implemented with a 75% reduction in the cost of the medication by using generic metformin, the cost per case of diabetes prevented during the trial and the cost per QALY gained would decrease by ~60% from either perspective.
From the perspective of a health system or society, what is the value of delaying or preventing type 2 diabetes? From a health system perspective, delaying or preventing type 2 diabetes delays or prevents the direct medical costs of diabetes, including the costs of diabetes education and nutritional counseling, glucose monitoring, treatment, surveillance of complications, and treatment of complications (19
). From a societal perspective, delaying or preventing diabetes reduces direct medical costs, out-of-pocket costs, and time lost from work (19
). It may also improve quality of life and length of life.
The direct medical costs of diabetes are enormous. It is estimated that per capita health care expenditures for individuals with diabetes are approximately $13,400 per year, $9,700 per year more than for individuals without diabetes (estimates adjusted to year-2000 U.S. dollars) (20
). These estimates probably overstate the actual initial costs of diabetes in DPP participants who developed diabetes, since they were very early in the clinical course and had few complications. The costs of diabetes increase with HbA1c
level and presence of complications and comorbidities (22
) and would be expected to be lower for individuals with lesser degrees of hyperglycemia and for those without complications. Nevertheless, costs are 2.1 times higher in patients with new clinically diagnosed diabetes compared with individuals without diabetes, and the incremental cost of diabetes is apparent from the time of diagnosis (21
). Compared with the substantial costs of diabetes, the costs per case of diabetes prevented seem quite reasonable, particularly when adjusted according to the most likely scenarios for clinical implementation.
If the treatment effects persist beyond 3 years, the costs per QALY gained of the lifestyle and metformin interventions over 3 years likely overstate the lifetime cost per QALY gained. By adopting a 3-year time horizon, the current economic analyses overestimate treatment costs and underestimate the benefits of the lifestyle and metformin interventions. The costs of both the lifestyle and metformin interventions are greatest in year 1 and decrease substantially in subsequent years (4
). Much of the benefit of both the lifestyle and metformin interventions will likely occur after 3 years of follow-up. It is likely that delaying or preventing type 2 diabetes will delay or prevent the need for treatment and delay or prevent the development of complications. It may also improve survival. These will translate into a relative decrease in treatment costs and an increase in QALY gained over a lifetime, substantially reducing the cost per QALY gained. However, estimating the long-term effects of the lifestyle and metformin intervention will require modeling costs and outcome beyond the time horizon of the DPP.
The results of the within-trial cost-utility analyses provide an assessment of the value of the lifestyle and metformin interventions relative to other interventions in medicine. Even with a 3-year time horizon, the costs per QALY gained of $9,000 to $29,000 for the lifestyle intervention and $35,000 for the metformin intervention, as they are likely to be implemented in clinical practice, fall within a range generally accepted as being cost-effective (23
). A recent report (24
) based on a simulation model has estimated that intensive glycemic control for patients with newly diagnosed type 2 diabetes in the U.S. costs approximately $41,000 per QALY gained over a lifetime. In patients with type 2 diabetes and a total cholesterol level ≥200 mg/dl, treatment with HMG-CoA reductase inhibitors costs $52,000 per QALY gained (24
). Published cost-utility ratios for interventions such as hypertension screening and therapy for asymptomatic 20-year-old men ($40,000 per QALY) are comparable (8
In summary, this 3-year within-trial economic analysis of the DPP demonstrated that the lifestyle and metformin interventions are cost-effective. These analyses should assist health plans and policy makers in comparing the benefit of diabetes prevention to other preventive and palliative interventions. The adoption of diabetes prevention programs in health plans will likely result in important personal and member benefits at a reasonable cost and over a short period of time. Further studies are needed to define the cost-utility of these interventions over a lifetime.