A sweeping national study with “enormous” public health implications has shown that controlling blood pressure more intensively can slow the debilitating progression of kidney disease in many African-American patients. The Miller School of Medicine serves as one of 22 U.S. medical centers taking part in the NIH’s African-American Study of Kidney Disease and Hypertension (AASK), which is designed to improve the health of thousands of African Americans who suffer disproportionately from kidney disease caused by hypertension.
According to the new study published in the September 2 issue of The New England Journal of Medicine, on average, a lower blood pressure goal was no better than the standard blood pressure goal at slowing progression of kidney disease among participants who had chronic kidney disease resulting from high blood pressure. However, a lower blood pressure goal did benefit a subset of patients who also had overt proteinuria, or protein in their urine.
The AASK found that among participants with overt protein in their urine, keeping blood pressure at the lower level not only reduced the likelihood of kidney disease progression, but also reduced kidney failure or death by 27 percent compared to the standard blood pressure level, a statistically significant difference. Patients who have overt proteinuria often have a more progressive form of kidney disease.
“For some patients, more intensive control of blood pressure may slow progression of chronic kidney disease,” said Griffin P. Rodgers, M.D., director of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) at the NIH. “Rigorous, long-term studies such as the AASK remain critically important for improving treatment of chronic kidney disease and other diseases that develop over time, as it can take years for benefits of treatment to emerge.”
The Miller School enrolled 60 participants, the eighth highest number in the country. AASK followed participants for approximately 12 years to measure the long-term effects of blood pressure control in African-Americans with kidney disease attributed to high blood pressure.
“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,” said Lawrence Appel, M.D., of Johns Hopkins University, Baltimore, 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.”
The study was conducted in two phases. First, in a clinical trial from 1995 to 1998, participants 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. After the clinical trial was completed, most of the remaining participants were enrolled in a follow-up study in which everyone had a blood pressure goal of less than 130/80 mm/Hg.
“The findings that a lower blood pressure level is very important in patients with overt proteinuria will change the way we treat these patients in the future,” said Gabriel Contreras, professor of medicine, co-author of the study, and principal investigator at the Miller School. “Protein in the urine is one of the best predictors of how fast you are going to progress to advanced kidney disease, and we now have a way in this group of patients to slow that progression. The public health implications of this study are enormous.”
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.
“For nearly two decades, the AASK research has provided valuable information about the most desirable, long-term chronic kidney disease treatment options for African-Americans, who bear a disproportionate burden of this debilitating disease,” said Lawrence Agodoa, M.D., director of the Office of Minority Health Research Coordination at the NIDDK. “People who participate in studies like AASK provide important information on how to protect the kidneys and preserve overall health.”
Study participants were initially recruited beginning in 1995 for the AASK Clinical Trial. Patients with diabetes and some other serious health problems were excluded. 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.
In the follow-up study, recommended blood pressure therapy started with an angiotensin converting enzyme (ACE) inhibitor. This medication works by blocking the action of the protein angiotensin, which raises blood pressure. If blood pressure was not controlled, additional drugs were added. On average, 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 trial was funded by NIDDK and additional support was provided by the NIH’s National Institute on Minority Health and Health Disparities, King Pharmaceuticals and other pharmaceutical companies that donated study drugs.