Background: The purpose of this study was to provide primary care physicians with a concise review of the evidence that guides selected aspects of type 2 diabetes care, including glycemic control, macrovascular risk reduction, and screening for microvascular complications of diabetes.
Methods: We identified randomized clinical trials that addressed selected aspects of the care of adults with type 2 diabetes using systematic literature review, review of existing clinical guidelines, and other sources. The results of these trials were interpreted as absolute risk reduction, and the number of patients that need to be treated to obtain a specific clinical outcome was calculated.
Results: Good glycemic control with metformin may reduce overall mortality in obese patients with type 2 diabetes (number need to treat [NNT] = 14 for 10 years), and improved blood pressure control reduced diabetes-related mortality (NNT = 15 for 10 years); improved glycemic control with agents other than metformin, or with combinations including metformin, does not reduce diabetes-related or overall mortality. Major cardiovascular events (CVE) in type 2 diabetes can be prevented by control of blood pressure with low-dose diuretics, atenolol, or angiotensin-converting enzyme inhibitors (NNT = 10 to 20 for 5 to 10 years for primary prevention of one CVE); by use of aspirin (NNT = 45 for 5 years for primary prevention of one CVE); and by use of simvastatin to lower low-density lipoprotein (LDL) cholesterol (NNT = 6 for 5 years for secondary prevention of one CVE). Glycemic control (NNT = 19 for 10 years) and hypertension control (NNT = 6 for 10 years) slow the progression of complications in patients with type 2 diabetes. Retinopathy and nephropathy are more preventable than neuropathy. The benefits of glycemic control are less for patients with shorter life expectancy and are greater for those with the highest levels of Hb A1c because larger Hb A1c improvements can be achieved in such patients. Periodic screening of patients for eye, kidney, and foot complications is supported because effective early treatment of these complications is available.
Conclusions: In patients with type 2 diabetes, control of hypertension reduces microvascular and macrovascular complications more than glycemic control does. Control of LDL cholesterol with statins, aspirin, and smoking cessation reduce major cardiovascular events. Metformin reduces overall mortality in obese patients with creatinine levels < 1.5 mg/dL. Glycemic control reduces microvascular complications. The evidence supports angiotensin-converting enzyme inhibitors, atenolol, or low-dose diuretics for blood pressure control. Effective treatment of eye, kidney, and foot complications is available, and regular screening for these complications is justified.