THURSDAY, Jan. 9, 2003 (HealthDayNews) -- Kidney disease is even more widespread than previously believed, a new study claims.
Nearly 8 million Americans, or 4 percent of U.S. adults, have lost more than half of their kidney function, the researchers report.
Another 6 percent, or 11 million adults, have the persistent presence of protein in their urine, one of the first signs that kidney disease is developing.
"The most important aspect of this study is we are now recognizing that moderate and severe kidney disease is quite common," says Dr. Josef Coresh, lead author of the study and an associate professor of epidemiology, medicine and biostatistics at Johns Hopkins Bloomberg School of Public Health.
The study appears in the January issue of the American Journal of Kidney Diseases.
Coresh and his colleagues analyzed health data from 15,625 U.S. adults who participated in the Third National Health and Nutrition Examination Survey (NHANES III).
One of the difficulties in quantifying kidney disease in the past had been the lack of a standardized system for classifying loss of kidney function, Coresh says.
Last year, Coresh was vice chairman of a committee of experts convened by the National Kidney Foundation that developed a standardized definition of kidney disease and five stages of severity.
Using the new guidelines, Coresh and his colleagues determined that 5.9 million Americans, or 3.3 percent of all adults, were at Stage 1. That means they had normal kidney function but had protein in their urine on two occasions.
About 5.3 million people, or 3 percent, were at Stage 2, with mildly decreased kidney function and protein in the urine on at least two occasions.
About 7.6 million people, or 4.3 percent, had Stage 3 kidney disease, meaning their kidneys filter less than half the amount filtered by a healthy young adult. An estimated one in five adults over the age of 65 are at Stage 3.
About 400,000, or 0.2 percent, had Stage 4 kidney disease. And 300,000, or 0.2 percent, had Stage 5 kidney failure, which occurs when the kidneys have lost 90 percent or more of their function.
Each day, healthy kidneys treat about 200 quarts of blood to remove about 2 quarts of waste products and extra water. The waste and extra water become urine, according to the National Institutes of Health.
People with end-stage kidney disease often require dialysis -- getting hooked up to a machine that purifies the blood because the kidneys can no longer do the job -- or a kidney transplant.
One of the obstacles in detecting kidney disease at its earliest stages is that there are few, if any, symptoms, says Dr. Tom Hostetter, director of the National Institutes of Health's National Kidney Disease Education Program.
"People don't feel sick until they've lost a lot of their kidney function," Hostetter says.
Early symptoms may include some fatigue or anemia, but nothing specific to the kidney, Coresh says.
To raise awareness of kidney disease, the National Institutes of Health has launched an education program. The pilot program will be unveiled in about six weeks in four U.S. cities: Atlanta; Baltimore; Cleveland and Jackson, Miss.
Hostetter and his colleagues are trying to get the word out about who's at risk for kidney disease.
About 40 percent of kidney failure is due to diabetes. Hypertension accounts for another 30 percent, Coresh says.
Blacks and Native Americans also have higher rates of kidney disease than whites and other races.
One part of the NIH education program will include radio spots and distributing educational brochures in doctor's offices and clinics. The NIH is also enlisting the help of local community leaders, who have come up with several ideas for spreading the word in their cities, including events such as walk-a-thons and health classes at churches.
A second crucial task of the education program is teaching laboratories how to better interpret kidney function tests, Hostetter says.
A simple blood test to measure levels of creatinine can identify kidney disease. High levels of creatinine are a marker that the kidneys aren't functioning properly, he says.
However, creatinine levels increase very slowly, so some laboratories and physicians have trouble interpreting the results, Hostetter says.
The NIH has developed equations that take into account several variables, including age, gender and race. When plugged into the equations, these factors can give a more clear-cut picture of how the kidneys are functioning.
Catching kidney disease early is crucial.
"There are so many things we can do to slow or even prevent kidney disease from progressing," Hostetter says. "But we can do the most when it's detected early."
What To Do
For more information on kidneys, visit the American Association of Kidney Patients or the National Kidney Foundation.
