The best available treatment for chronic kidney disease from high blood pressure did not keep the disease from substantially worsening in about a fourth of African-Americans studied, according to long-term results of a National Institutes of Health study published  in the Archives of Internal Medicine.

The largest and longest study of chronic kidney disease in African-Americans — the African American Study of Kidney Disease and Hypertension (AASK) — found that the disease substantially worsened in about one-fourth of participants, even with very good blood pressure control and use of kidney-protecting medications, currently the best available treatment.

This subgroup of patients either lost half their kidney function or reached kidney failure, also known as end-stage renal disease.

"Despite these sobering results, blood pressure control is still vital in kidney disease and in many other diseases," said NIH Director Elias A. Zerhouni, M.D.

"But this research clearly signals the importance of preventing kidney disease, better understanding causes and finding better ways to manage it in the 26 million Americans who already have it."

Good news also emerged from the study. About one-third of participants experienced a slow decline in kidney function, about what is generally observed with aging.

 "The factors that may be responsible for such a small loss of kidney function need to be studied," said Lawrence Y. Agodoa, M.D., senior author of the study and director of kidney failure research at NIH’s National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), which funded the study.

The AASK Cohort Study observed about 750 African-Americans on recommended therapy for chronic kidney disease from 2002 to 2007.

Study participants were initially recruited beginning in 1995 for the AASK Clinical Trial www.nih.gov/news/pr/nov2002/niddk-25.htm, which concluded in 2001 that an ACE inhibitor medication protected the kidneys better than two other classes of blood pressure drugs.

During the Cohort Study, nearly 9 out of 10 participants were taking an ACE inhibitor or an angiotensin receptor blocking drug, and average blood pressure was 133/78 mmHg, close to national guidelines for high blood pressure in people with chronic kidney disease.

Uncontrolled high blood pressure, an increase in the number of people with diabetes, and the aging of the U.S. population means more people than ever are getting and living with kidney problems.

About 13 percent of the U.S. population, up from 10 percent in 1994, now have chronic kidney disease.

And in 2005, more than 485,000 people were on chronic dialysis or had a kidney transplant for kidney failure, costing Medicare, private insurers and patients $32 billion.

Diabetes and high blood pressure are leading causes of kidney disease, which runs in families and disproportionately affects African-Americans and American Indians.

The condition can lead to kidney failure, premature death, heart attacks, strokes, bone disease, and growth and developmental problems in children.

Blood and urine tests are the only way to find kidney disease early, when treatment is more likely to significantly delay or prevent kidney failure.

Important therapies that help protect the kidneys include careful control of high blood pressure — and blood sugar in people with diabetes — ACE (angiotensin-converting enzyme) inhibitors or ARBs (angiotensin receptor blockers) to reduce protein in the urine, and therapies to reduce the risk of cardiovascular disease, which increases the risk of developing kidney disease.

Learn more about early detection and treatment from NIDDK’s National Kidney Disease Education Program at www.nkdep.nih.gov or by calling toll-free 1-866-4-KIDNEY (1-866-454-3639).

The AASK Trial and Cohort Study were conducted at 21 U.S. medical centers and have been funded by NIDDK since 1994. Additional support was provided by NIH’s National Center on Minority Health and Health Disparities and by King Pharmaceuticals.

The National Institute of Diabetes and Digestive and Kidney Diseases, a component of the NIH, conducts and supports research in diabetes and other endocrine and metabolic diseases; digestive diseases, nutrition, and obesity; and kidney, urologic, and hematologic diseases.

 Spanning the full spectrum of medicine and afflicting people of all ages and ethnic groups, these diseases encompass some of the most common, severe, and disabling conditions affecting Americans.

For more information about NIDDK and its programs, see www.niddk.nih.gov.

The National Institutes of Health (NIH) — The Nation's Medical Research Agency — includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical and translational medical research, and it investigates the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov