This Physician’s Weekly feature on chronic kidney disease and diabetes was completed in cooperation with the experts at the American Diabetes Association.
Each year in the United States, more than 100,000 people are diagnosed with kidney failure, and diabetes is the most common cause of it, accounting for nearly 44% of new cases. Even when diabetes is controlled, it can lead to chronic kidney disease (CKD) and kidney failure. “According to current estimates, about 20% to 30% of people with diabetes have at least some CKD, although not necessarily end-stage renal disease,” explains M. Sue Kirkman, MD. “More patients with diabetes also have very early signs of kidney damage, such as microalbuminuria. Fortunately, we now have interventions to help prevent early CKD from progressing or worsening in people with diabetes.”
Diabetic kidney disease takes many years to develop. In some patients, the filtering function of the kidneys is higher than normal in the first few years of the development of diabetes. Over several years, patients may develop low levels of albuminuria—termed microalbuminuria—but the kidneys’ filtration function usually remains normal during this period. Greater amounts of albuminuria (macroalbuminuria) occur in parallel with the kidneys’ filtering function declining, forcing the body to retain various wastes along the way. As kidney disease progresses, physical changes in the kidneys can increase blood pressure. As such, early detection and treatment of even mild hypertension are essential for people with diabetes.
Early Screening is Imperative
The American Diabetes Association recommends that every patient diagnosed with diabetes be screened for CKD (Table 1). “It’s better to diagnose it early and address problems at that time rather than waiting until more advanced CKD develops,” says Dr. Kirkman. The American Diabetes Association recommends administering an annual urine albumin assessment and a serum creatinine test with a calculation of the estimated glomerular filtration rate (eGFR). The annual urine albumin assessment is typically a spot urine albumin-to-creatinine ratio. The serum creatinine and eGFR are tested to measure kidney function. “This second test is important because there is a fair amount of CKD that is not accompanied by albuminuria in patients with type 2 diabetes,” Dr. Kirkman says. “Simply looking for albumin excretion alone is probably not sufficient to catch kidney disease.”
A key part of screening for CKD in patients with diabetes is to become aware of the risk factors for it. Patients with longer duration of diabetes, poorly controlled diabetes for long periods of time, and uncontrolled hypertension are at greater risk for CKD than others. Smoking and obesity have also recently been identified as risk factors for CKD. In addition, African Americans, Native-American, and Hispanics/Latinos tend to have a higher risk for CKD than other racial and ethnic groups. “When physicians see patients with these risk factors, it’s important for them to be screened as early as possible for CKD,” says Dr. Kirkman. “If kidney disease is detected, it should be addressed as part of a comprehensive approach to the treatment of diabetes.”
Interventions Can Prevent or Slow Kidney Disease
Great strides have been made in the development of interventions that slow the onset and progression of kidney disease in people with diabetes, and antihypertensive medications have been particularly useful. “Two types of medications—ACE inhibitors and angiotensin receptor blockers (ARBs)—have proven effective in slowing the progression of CKD,” Dr. Kirkman says (Table 2). It should be noted that many people require two or more drugs to control their blood pressure. In addition to an ACE inhibitor or an ARB, a diuretic can also be helpful. Other classes of drugs, including b-blockers, calcium channel blockers, and other antihypertensives, may also be needed. ACE inhibitors and ARBs not only lower blood pressure, but they also help protect the kidneys’ glomeruli. These medications lower proteinuria and slow kidney deterioration even in people with diabetes who do not have high blood pressure. Both classes may also lower the risk of cardiovascular events.
Excessive consumption of protein may be harmful to the kidneys, so experts recommend that people with CKD resulting from diabetes consume no more than the recommended dietary allowance for protein and avoid high-protein diets. For people with greatly reduced kidney function, a diet containing reduced amounts of protein may help delay the onset of kidney failure.
Aim for Good Glycemic Control
Research has also demonstrated that intensive glycemic control benefits patients with diabetes, especially for preventing onset or progression of the early stages of CKD. “Once kidney disease is more advanced, intensive glycemic control may not have an impact, but good blood pressure control is critical to slowing decline in kidney function,” says Dr. Kirkman. “In the future, it’s hoped that we’ll discover ways to more effectively predict which patients will develop CKD so that prevention and treatment strategies can be enhanced.”
Kidney Disease of Diabetes. National Institute of Diabetes and Digestive and Kidney Diseases. Available at: http://kidney.niddk.nih.gov/kudiseases/pubs/kdd/.
United States Renal Data System. USRDS 2007 Annual Data Report. Bethesda, MD: National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, U.S. Department of Health and Human Services; 2007.
National Institute of Diabetes and Digestive and Kidney Diseases. National Diabetes Statistics, 2007. Bethesda, MD: National Institutes of Health, U.S. Department of Health and Human Services, 2008.
American Diabetes Association. Standards of Medical Care—2010. Diabetes Care. 2010;33(Suppl 1):S11-S61. Available at: http://care.diabetesjournals.org/content/33/Supplement_1/S11.full.
James MT, Hemmelgarn BR, Tonelli M. Early recognition and prevention of chronic kidney disease. Lancet. 2010;375:1296-1309.