Research Updates in Kidney and Urologic Health
NIDDK Calculation Leads to New Estimates of Kidney Disease Prevalence, Treatment Recommendations
Millions of Americans have chronic kidney disease (CKD) without knowing they have it. Hundreds of thousands will progress to kidney failure because they did not take steps to slow or arrest the decline of their kidney function. These findings prompted the National Kidney Foundation (NKF) to release clinical practice guidelines to support routine screening for CKD, especially among populations at high risk—African Americans, people with diabetes, people with high blood pressure, and family members of patients with kidney disease.
Three Easy Tests
The guidelines, released in February 2002, call for three easy and inexpensive tests to be performed routinely: a spot check for protein in the urine, a calculation of glomerular filtration rate (GFR) based on a serum creatinine value, and a blood pressure measurement. Most physicians perform these tests during regular physical exams, but abnormal results indicating kidney damage are often ignored or are not followed up adequately.
Measuring GFR used to require a 24-hour urine collection as well as a blood sample. But researchers in the Modification of Diet in Renal Disease trial sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) developed a GFR calculation that requires only a serum creatinine value along with the patient's weight, race, and sex. The CKD Work Group urges laboratories to perform the calculation as a routine service.
"Americans who have diabetes, high blood pressure, or a family history of kidney disease should ask their physicians for routine blood and urine tests to diagnose chronic kidney disease," urged NKF president William F. Keane, M.D., at a press conference to announce the publication of the guidelines in the February issue of the American Journal of Kidney Diseases. "These tests can detect chronic kidney disease in its early stages when lifestyle changes and medication can be prescribed to delay or prevent the progression of kidney disease and its complications, including the development of heart disease."
Effective Treatments Available
"Recent research indicates that kidney failure can be prevented or delayed if chronic kidney disease is diagnosed early enough in its progression and treated properly," said Andrew S. Levey, M.D., chair of the work group that developed the evidence-based guidelines.
Treatments shown to slow the decline of kidney function include blood pressure medicines that block or inhibit action of the angiotensin system. ACE (angiotensin-converting enzyme) inhibitors were first approved in the early 1990s to protect against nephropathy in patients with type 1 diabetes. Later research showed that the renoprotective effects of ACE inhibitors extended to patients with type 2 diabetes and to patients who did not have diabetes but who had reduced kidney function. More recently, angiotensin-2 receptor blockers (ARBs) have also been found to reduce proteinuria and protect the kidneys.
The NKF guidelines call for the close monitoring and strict control of blood pressure and blood glucose in patients with diabetes. Some evidence supports restricting protein in the diet to decrease the burden on the kidneys, but this strategy has not been shown to work for every patient, and great care must be taken with this diet to avoid malnutrition.
CKD Defined
In the past, researchers have had problems estimating the prevalence of CKD because no precise definition existed. The new guidelines define CKD as a GFR that remains below 60 mL/min/1.73 m2 for more than 3 months. "Our new definition provided us with criteria for analyzing data from the third National Health and Nutrition Examination Survey and calculating the first-ever prevalence figures for each stage of the disease," said Dr. Levey, who is professor of medicine at the Tufts University School of Medicine and chief of nephrology at the New England Medical Center in Boston. The new calculation indicates that 20 million Americans have CKD.
Stages of Disease Outlined
The new guidelines identify five stages of CKD and recommend actions to take at each stage.
- Stage 1 includes 5.9 million patients who have kidney damage but a normal GFR (90 or higher). The recommended actions are to diagnose and treat the cause of the kidney damage, treat comorbid conditions, slow the progression of CKD, and reduce cardiovascular risk factors.
- Stage 2 includes 5.3 million patients with mild GFR reduction (60-89). The recommended action is to estimate disease progression.
- Stage 3 includes 7.6 million patients with moderate GFR reduction (30-59). The recommended actions are to evaluate and treat complications such as anemia and bone disease.
- Stage 4 (400,000 patients) is severe GFR reduction (15-29). The recommended action is to prepare the patient for kidney replacement therapy.
- Stage 5 (300,000 patients) is kidney failure, marked by a GFR below 15. The recommended action is to initiate kidney replacement therapy—either dialysis or transplantation—if uremia is present.
Because too few nephrologists are available to care for the entire population of patients with CKD, these guidelines will help general practitioners manage patients during the early stages of the disease.
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