Implications of the Diabetes Control and Complications Trial

The DCCT is a landmark multicenter trial designed to test the proposition that the complications of diabetes mellitus are related to elevation of the plasma glucose concentration. The study design was simple. Two groups of patients were followed long term, one treated conventionally (goal: clinical wellbeing; called standard treatment group) and another treated intensively (goal: normalization of blood glucose; called intensive treatment group). The intensive treatment group was clearly distinguished from the standard treatment group in terms of glycated hemoglobin levels and capillary blood glucose values throughout the duration of the study. Normalization of glucose values was not achieved in the intensively treated cohort as a group because mean glucose values were —40% above normal limits. Nonetheless, over the study period, which averaged 7 years, there was an ~60% reduction in risk between the intensive treatment group and the standard treatment group in diabetic retinopathy, nephropathy, and neuropathy. The benefit of intensive therapy resulted in a delay in the onset and a major slowing of the progression of these three complications. Finally, the benefits of intensive therapy were seen in all categories of subjects regardless of age, sex, or duration of diabetes. The American Diabetes Association believes that the study has both statistical and clinical significance. The DCCT is the longest and largest prospective study showing that lowering blood glucose concentration slows or prevents the development of diabetic complications. As such, it has major therapeutic implications for health-care providers and their patients. Many questions remain to be answered, but the following conclusions appear warranted: 1. A primary treatment goal in IDDM should be blood glucose control at least equal to that achieved in the intensively treated cohort. This goal may not apply to all patients with IDDM and must be based on clinical judgment. Of importance, intensively treated patients had a three-fold greater risk of hypoglycemia than did patients in the control group. Because serious hypoglycemia is dangerous, "tight" control goals may have to be sacrificed in people in whom frequent or severe hypoglycemia cannot be avoided by treatment modification. 2. It is not known for certain whether the results obtained in this study of people with IDDM apply to people with NIDDM. Nonetheless, it seems reasonable to recommend tight control in many patients with noninsulin-dependent disease because it is presumed that the mechanisms by which glucose causes complications is the same in both forms of diabetes. However, because there may be other medical conditions in people with NIDDM, tight control may not be appropriate for all people with this type of diabetes. 3. There is no favored form of treatment to achieve tight control of blood glucose levels. The decision to use multiple injections of insulin versus an insulin pump depends on the preference of the patient with IDDM and the ability of the healthcare team to provide the necessary resources and support. In NIDDM, diet, exercise, and oral drugs may achieve tight control, but insulin is often required.