10 to 20 million people in the United States have chronic kidney disease but most don’t know it

10 to 20 million people in the United States have chronic kidney disease but most don’t know it, according to a study by researchers at the Johns Hopkins Bloomberg School of Public Health, the National Institute of Diabetes and Digestive and Kidney Diseases and the National Center for Health Statistics. The findings are published in the January 2005 print edition of the Journal of the American Society of Nephrology and on the journal’s website.

Over the past decade the number of people with kidney failure doubled and the number starting dialysis or having a first kidney transplant increased by 50 percent, so that more than 400,000 Americans are now being treated for kidney failure at a cost of $25 billion annually. In contrast to these dramatic increases, the study found that the number of people with earlier stages of kidney disease remained stable, with 7.4 million people having less than half the kidney function of a healthy young adult and another 11.3 million consistently having protein in their urine. The researchers can’t explain this paradox, but suggest that fewer patients may be dying and more may be progressing to dialysis faster.

“Given the high prevalence of chronic kidney disease, we need to increase awareness, diagnosis and treatment if we are going to reduce the rate of progression and complications. Most critical are control of diabetes and hypertension.” said Josef Coresh, MD, PhD, lead author of the study and professor of epidemiology, medicine and biostatistics at the Bloomberg School of Public Health.

Dr. Coresh and his colleagues estimated awareness of chronic kidney disease among 4,101 people in the United States from 1999 to 2000 and compared disease prevalence in those years with that from 1988 to 1994, when 15,488 people were surveyed. Data were from two National Health and Nutrition Examination Surveys by NCHS of nationally representative, non-institutionalized adults.

In the recent survey participants were asked: “Have you ever been told by a doctor or other health professional that you had weak or failing kidneys (excluding kidney stones, bladder infections, or incontinence)?” Less than 10 percent of adults with moderately decreased kidney function (one half to one quarter the filtering capacity of a young healthy adult) reported being told they had weakened or failing kidneys. Awareness was low in all but the most severe stages of kidney disease. Women with moderately decreased kidney function were significantly less aware of their illness compared to similarly affected men.

Lack of awareness may be due in part to most doctors’ sole reliance on a test that measures the blood level of a substance called creatinine. Unfortunately, the test is affected by muscle mass and other person-to-person variables. “Most blood tests include creatinine, but the numbers can be misleading. Kidney disease can be quite advanced before it’s found this way.” said Thomas H. Hostetter, MD, senior study author and director of NIDDK’s National Kidney Disease Education Program (NKDEP). NKDEP recommends that doctors take creatinine a simple step further to estimate glomerular filtration rate (GFR). GFR is a more accurate gauge of how well the kidneys are working.

“We can use a patient’s creatinine number, age, gender and race to estimate GFR and find kidney disease earlier, when there’s still time to treat it. A free GFR calculator makes estimating a snap.” said Dr. Hostetter. NKDEP is also working to make the task even easier for busy physicians. “We are very pleased that several major labs have agreed to automatically report GFR whenever creatinine is measured. We are still working quite hard to standardize tests for kidney disease by all labs.”

People with chronic kidney disease are at high risk for premature death, heart attacks and strokes as well as hypertension, anemia, bone disease and malnutrition. NKDEP strives to increase awareness about kidney disease and offers the GFR calculator and other free tools at www.nkdep.nih.gov.