Chronic Kidney Disease Prevalence Creeps Up

ATLANTA, March 2 --The prevalence of chronic kidney disease appears to be on the rise, according to CDC researchers.

In the period from 1999 to 2004, 16.8% of the U.S. population ages 20 and older had chronic kidney disease, up from 14.5% in the period from 1988 to 1994, wrote Sharon Saydah, Ph.D., of the National Center for Chronic Disease Prevention and Health Promotion, and colleagues. The difference represents a 15.9% increase based on crude estimates of prevalence.

As would be expected, the prevalence of chronic kidney disease was greater among older men and women, and among those with diabetes, cardiovascular disease, and hypertension, the investigators wrote in the March 2 issue of the Morbidity and Mortality Weekly Report.

In addition, Mexican Americans and non-Hispanic blacks had a greater prevalence of chronic kidney disease, particularly stage 1 disease, than non-Hispanic whites.

"The large disparity in prevalence among those with stage 1 chronic kidney disease might be explained, in part, by racial/ethnic differences in microalbuminuria among non-Hispanic blacks and Mexican Americans," the MMWR editors wrote in an explanatory commentary.

According to the CDC, both the incidence and prevalence of end-stage renal disease have increased during the past 30 year, and both are expected to continue increasing through the year 2010.

The investigators estimated the prevalence of chronic kidney disease in the United States using the most recent data from the National Health and Nutrition Examination Survey (NHANES). They looked at overall prevalence of chronic kidney disease, and also the prevalence broken down by risk factors and demographics.

"Persons with diabetes or cardiovascular disease had a greater prevalence of chronic kidney disease than persons without those conditions," the investigators wrote. "These results underscore the need to continue surveillance for chronic kidney disease and its risk factors in the United States and to implement new strategies to reduce the number of persons with this condition."

The investigators assembled their estimates from three consecutive NHANES surveys, each of which spanned two years. The survey is a continuous and large-scale sample of the health and nutritional status of the US civilian, non-institutionalized population.

NHANES investigators conduct interviews in participants' homes, and perform medical examines in mobile examination center to gather data for the survey.

To determine chronic kidney disease prevalence, the report's authors looked at serum creatinine, as well as urine albumin and creatinine from a single spot urine test.

The category of apparent kidney damage (stage 1 and 2) included patients with microalbuminuria, defined as an albumin-to-creatinine ratio of 17-250 mg/g for men or 25-355 mg/g for women, and macroalbuminuria, defined as a ratio of >250 mg/g for men or >355 mg/g for women.

They estimated levels of kidney function by glomerular filtration rate (GFR), with lower values corresponding to diminished kidney function.

They then estimated chronic kidney disease prevalence from apparent kidney damage and diminished kidney function, and categorized them into stages, with increasing stage numbers corresponding to increased severity, according to the National Kidney Foundation classification system.

They calculated chronic kidney disease prevalence by demographic characteristics, including age, gender, race/ethnicity, and education level, and by chronic kidney disease risk factors: diagnosed diabetes (based on self-report of a clinician's diagnosis) cardiovascular disease (defined as self-report of diagnosis by a doctor or other health professional of congestive heart failure, coronary heart disease, angina, stroke, or heart attack), hypertension, and body mass index.

The estimated prevalence rates by disease stage were:

• Stage 1: 5.7%
• Stage 2: 5.4%
• Stage 3: 5.4%
• Stages 4/5: 0.4%

Among those 60 and older, the prevalence of chronic kidney disease (all stages was 39.4%. In comparison, the prevalence was 12.6% among 40- to 59-year-olds, and 8.5% among 20- to 39-year-olds.

The prevalence of disease was also higher among people who did not graduate from high school compared with high school graduates and those attaining higher levels of education, at 22.1% versus 15.7%.

Among those with diabetes, chronic kidney disease prevalence was 40.2% versus 15.4% for non-diabetics. More than one-fourth of people with cardiovascular disease (28.2%) had chronic kidney disease, compared with 15.4% of people without cardiovascular disease. And people with hypertension had twice the rate as those with normal blood pressure, at 24.6% versus 12.5%.

"In addition, chronic kidney disease prevalence was greater among non-Hispanic blacks (19.9%) and Mexican Americans (18.7%) than among non-Hispanic whites (16.1%)," the investigators wrote. "This racial/ethnic disparity was most pronounced among participants with stage 1 CKD. In that group, Mexican Americans had a prevalence of 10.2% and non-Hispanic blacks had a prevalence of 9.4%, compared with 4.2% for non-Hispanic whites."

The MMWR editors noted that the findings are subject to several limitations, including the use only of albuminuria (and not urine sediment or renal imaging) to determine kidney damage in people with early-stage disease. The latter tests are not included in NHANES data, suggesting that the actual incidence of disease could be higher than the estimates.

Conversely, because the evaluations were based on just one urine sample rather than two, and because previous analyses showed that repeat urine samples result in lower stage 1 and 2 prevalence rates, it's also possible the current survey over-estimated the prevalence.

"New programs aimed at decreasing the number of chronic kidney disease cases were established recently," the MMWR editors noted. "The National Kidney Disease Education Program provides resources to the public, patients, and health-care professionals with the goal of reducing morbidity and mortality from kidney disease complications. World Kidney Day was instituted in 2006 to increase awareness of kidney disease and promote early detection. Continued surveillance of albuminuria and serum creatinine using NHANES can track the prevalence of chronic kidney disease, monitor trends, and identify groups at high risk, enabling targeted programs."

The CDC is working with Johns Hopkins and the University of Michigan to develop a comprehensive national surveillance system for chronic kidney disease that will monitor early stages of the disease and its risk factors and the effects of chronic kidney disease on the U.S. population.