Background: Obesity is highly prevalent among patients with type 2 diabetes. Unfortunately, weight gain may also be a consequence of some antidiabetic medications. Although clinical benefits of weight loss have been established, the economic consequence of weight change among patients with type 2 diabetes is unclear Objectives: The objective was to measure 1-year total and d iabetes-related health care costs associated with weight change during the preceding 6-month period among type 2 diabetic patients on antidiabetic therapy. Methods: Administrative claims, electronic laboratory data and medical chart information were abstracted for continuously enrolled adults with type 2 diabetes from an health maintenance organization (HMO) for the period from July 1, 1997 through October 31, 2005. To assess the economic impact of weight change, three regression models were applied to estimate the following: (1) the effect of weight change in general (one-slope model); (2) the different effects of weight gain and no weight gain (two-slope model); and (3) the different effects of weight gain and no weight gain (i.e., no change or weight loss) among obese and non-obese patients (four-slope model). Patients included in the study had a baseline weight measurement and a second weight measurement approximately 6 months later. They were also required to be on at least one antidiabetic drug therapy within 1 month around the baseline weight measurement date (index date). Based on the measured weight change, patients were classified into two groups-weight gainers and non-weight gainer. Total health care cost and diabetes-related cost were measured during the 1-year period following the second weight measurement and were adjusted to 2004 dollars by the medical component of the Consumer Price Index (CPI). Generalized linear models with log link function and gamma distribution were applied to assess the impacts of weight change on the 1-year total health care cost as well as 1-year d iabetes-related cost. All models controlled for patients' baseline demographics, comorbidities, body mass index (BMI), glycosylated hemoglobin (HbA(1c)), and prior resource utilization. Results: The study included 458 patients, of whom 224 (48.9%) experienced minimum weight gain of 1 pound between the two weight measurements. The average 1-year total health care cost following the second weight measure was $6382 and the d iabetes-related cost was $2002. The mean total health care cost was $7260 for the weight-gainers and $5541 for the non-weight gainers (p = 0.046), and the mean diabetes-related cost, respectively, was $2141 and $1869 (p = 0.006). Results from the models showed that one percentage point of weight change was positively associated with a 3.1 % ($213, p < 0.01) change in total health care cost. When weight gain and no gain were modeled separately, one percentage point of weight loss was associated with a 3.6% ($256, p < 0.05) decrease in total health care cost and a 5.8% ($131, p < 0.01) decrease in d iabetes-related cost. However, one percentage point of weight gain was not associated with significant increase in either total health care or d iabetes-related cost. Further, results from the model with interactions between weight change and obesity status revealed that the economic benefit of weight loss was more pronounced in the obese group (BMI >= 30). Log likelihood ratio tests showed that the one-slope model for total health care cost and the two-slope model for diabetes-related cost are the appropriate models of choice. Conclusions: Weight loss significantly reduced diabetes-related costs. Controlling for baseline factors in the regression model, the 1-year total health care cost following 1 % weight loss (or gain) was $213 cost decrease (or increase). Diabetes-related cost did not appear to be associated with weight gain. Economic benefit of weight loss was evident among type 2 diabetic patients on antidiabetic therapy, especially among obese patients.
