19.2 Million U.S. Adults Have Chronic Kidney Disease

Of the five categorical stages, with Stage 5 being kidney failure, the largest number of adults, 7.6 million or 4 percent of adults, are classified in Stage 3 in which their glomerular filtration rate (GFR) is 30-59 ml/min/1.73m2. This means that the kidneys filter less than one-half of the amount filtered by a healthy young adult of a similar body size (130 ml/min or 2 gallons/hour). As a result, the kidneys are less efficient at removing toxins and secreting hormones important for healthy blood and bone function. The presence of chronic kidney disease can be detected using simple blood and urine tests relying on serum creatinine to estimate kidney function and urinary albumin to indicate kidney damage.

Josef Coresh, MD, PhD, lead author of the study and associate professor of epidemiology, medicine, and biostatistics at the Johns Hopkins Bloomberg School of Public Health, said, "As the population ages, kidney disease will become more apparent. However, there is already a growing recognition of the importance of moderate and severe chronic kidney disease, prior to the onset of kidney failure requiring dialysis, as an important treatable condition. We estimate that 4 percent of U.S. adults, approximately 8 million people, have less than half of the normal kidney function of a young adult. This low level of kidney function is estimated to be present in one out of every five Americans over the age of 65. Another 11 million adult Americans have a persistent presence of at least a small amount of albumin (the main protein in blood) in their urine." Dr. Coresh explained that patients with chronic kidney disease are at a high risk of heart attacks and strokes. They also have treatable conditions such as hypertension, anemia, and poor nutritional status.

Researchers used the recently developed National Kidney Foundation Clinical Practice Guidelines which provide a standardized definition of chronic kidney disease and its stages to a nationally representative sample of 15,625 non-institutionalized adults who participated in the Third National Health and Nutrition Examination Survey (NHANES III). Participants were also interviewed about their history of diabetes and hypertension. Chronic kidney disease stages are based on estimated kidney function measured as GFR. A healthy young adult has a GFR of 130 ml/min/1.73 m2. The researchers found an estimated 5.9 million individuals (3.3%) had Stage 1/normal kidney function with protein found in urine on two occasions; 5.3 million (3%) had Stage 2/ mildly decreased kidney function with protein found in urine on two occasions; 7.6 million (4.3%) had Stage 3/moderately decreased kidney function (GFR 30-59 ml/min/1.73 m2); 400,000 (0.2%) had Stage 4/severly decreased kidney function (GFR 15-29 ml/min/1.73 m2); and 300,000 (0.2%) had Stage 5 or kidney failure.

Older age was strongly associated with a higher prevalence of moderately or severely decreased kidney function. In addition, moderately decreased kidney function was most prevalent among non-Hispanic whites, followed by non-Hispanic blacks, then individuals of other ethnicities. Kidney disease was least prevalent in Mexican Americans. These results also raise the possibility that minority populations have a higher risk of kidney failure because of more rapid progression of kidney disease after its onset, rather than a larger pool of individuals with milder kidney disease.

The study estimates of decreased kidney function far exceed the number of cases of treated end-stage renal disease. Over 340,000 patients required dialysis or transplantation in 1999. That number is expected to increase to 651,000 by 2010. Previous studies of patients' medical charts indicate that many patients are going undiagnosed and under-treated in the early stages of kidney disease.

Coresh, also a faculty member in the Johns Hopkins Welch Center for Prevention, Epidemiology & Clinical Research, said, "By using standardized criteria and carefully calibrated estimates of kidney function, national prevalence estimates of chronic kidney disease can be a benchmark for future studies and international comparisons. Such efforts are critical to improving diagnosis, treatment, and prevention of CKD and its complications."

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"Prevalence of Chronic Kidney Disease and Decreased Kidney Function in the Adult U.S. Population: Third National Health and Nutrition Examination Survey" will appear in the January 2003, issue of the American Journal of Kidney Diseases.

Brad C. Astor, Ph.D., MD, MPH, an assistant professor in the School's Department of Epidemiology co-authored the study.

Additional authors were Tom Greene, Ph.D., with the Cleveland Clinic Foundation, Garabed Eknoya, MD, with Baylor College of Medicine, and Andrew S. Levey, MD, with Tufts University School of Medicine.

Research was supported by grants from the National Institutes of Health, the National Kidney Foundation, and the Johns Hopkins General Clinical Research Center.

Link to the Johns Hopkins Bloomberg School of Public Health at http://www.jhsph.edu .