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Blood Pressure and Kidney Disease in African-Americans

A lower blood pressure goal was no better than the standard goal at slowing the progression of kidney disease among African-Americans with chronic kidney disease resulting from high blood pressure. However, the findings suggest that the blood pressure goal did benefit people who also had protein in the urine, which is a sign of kidney damage.

In the United States, high blood pressure causes about one-third of new cases of kidney failure, also known as end-stage renal disease. The cost to the government and private payers for end-stage renal disease now exceeds $35 billion annually.

African-Americans bear a disproportionate burden of this debilitating disease. The African-American Study of Kidney Disease and Hypertension (AASK) is the largest and longest study of chronic kidney disease in African-Americans. The study was conducted in 2 phases beginning in 1995. First, in a clinical trial, participants at 22 U.S. medical centers were randomly assigned to a standard blood pressure goal of roughly 140/90 mmHg (usual) or a lower goal of less than 130/80 mmHg. The initial AASK trial yielded important insights into blood pressure, hypertension medications and kidney disease.

After the conclusion of that study, AASK participants who had not yet developed end-stage renal disease were invited to participate in the AASK follow-up study, which started in 2002. The AASK trial and the follow-up study were funded by NIH's National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), with additional support from NIH's National Institute on Minority Health and Health Disparities (NIMHD), King Pharmaceuticals and other pharmaceutical companies.

In the follow-up study, most patients were given an angiotensin converting enzyme (ACE) inhibitor in addition to other drugs to control their blood pressure. ACE inhibitors work by blocking the action of the protein angiotensin, which raises blood pressure. If blood pressure remained high, additional drugs were added. On average, the patients needed about 3.5 medications for blood pressure each day. Millions of Americans take the drugs used in this study or drugs like them to treat health problems such as high blood pressure or heart disease. The patient follow-up ranged from about 9 to 12 years.

The results appeared in the September 2, 2010, issue of the New England Journal of Medicine. The researchers found that, overall, a lower blood pressure goal was no better than the standard goal at slowing progression of kidney disease. However, among people with protein in their urine, a lower blood pressure level reduced the likelihood of kidney disease progression, kidney failure or death by 27% compared to the standard level.

"For some patients, more intensive control of blood pressure may slow progression of chronic kidney disease," says NIDDK Director Dr. Griffin P. Rodgers.

"The AASK study is the largest and longest study of kidney disease in African-Americans. It is a landmark study that is paying off—guiding patient care and improving health outcomes," says Dr. Lawrence Appel of Johns Hopkins University, who chaired the study. "This study also highlights the importance of conducting long-term clinical studies. Without the follow-up study, the benefits of the lower goal would have been missed."