Continuation of AASK Cohort Study

• Background
• Continuation of AASK Description
• Study Inventory

Background

African Americans are disproportionately afflicted with end-stage kidney failure, also known as end-stage renal disease (ESRD). Although they constitute approximately 12 percent of the U.S. population, African Americans comprise 32 percent of the prevalent ESRD population. In African Americans, especially, hypertension is a major cause of ESRD. The racial disparity is most striking in young African Americans, ages 25 to 44, who are 20 times more likely than whites of that age group to develop kidney failure caused by high blood pressure.

Although better management of high blood pressure has led to a decline in the number of people who develop strokes and heart disease, the number of people developing kidney failure has increased. In 1990, the NIDDK launched an initiative to investigate the underlying cause of ESRD and to study mechanisms that could slow progression of hypertensive kidney disease in African Americans. The clinical trial, African American Study of Kidney Disease and Hypertension (AASK), was initiated to investigate whether a specific class of antihypertensive drugs (beta-adrenergic blockers, calcium channel blockers, or angiotensin converting enzyme inhibitors) and/or the level of blood pressure (a mean arterial pressure or MAP of 102-107 mm Hg, or a MAP of 92 mm Hg) would influence progression of hypertensive kidney disease in African Americans.

After a brief period of pilot study (1992-1994), 20 clinical centers and a data-coordinating center were funded to carry out the full-scale clinical trial in 1994. The twenty-first clinical center was added in June 1996. As in the pilot clinical trial, all four historically black medical schools were funded to participate in the full-scale trial. The centers required nine months to revise the protocol for the full-scale trial, and participant recruitment and randomization began in April 1995. The intervention component ended in March 2002, and the primary analysis of the study results concluded in June 2002.

In 2001, a significant discovery was made in the treatment strategy for slowing kidney disease caused by hypertension. Angiotensin-converting enzyme (ACE) inhibitors, compared with calcium channel blockers, were found to slow kidney disease progression by 36 percent, and they drastically reduced the risk of kidney failure by 48 percent in patients who had at least one gram of protein in the urine, a sign of kidney failure. ACE inhibitors have been the preferred treatment for hypertension caused by diabetes since 1994; however, calcium channel blockers have been particularly effective in controlling blood pressure in African Americans. The AASK study now recommends ACE inhibitors to protect the kidneys from the damaging effects of hypertension.

Continuation of AASK Description

The Continuation of AASK Cohort Study was initiated at the conclusion of the AASK Intervention Study. The primary goal of the Continuation of AASK Cohort Study is to investigate the environmental, socio-economic, genetic, physiologic, and other co-morbid factors that influence progression of kidney disease in a well-characterized cohort of African Americans with hypertensive kidney disease.

The Continuation of AASK Cohort Study will be followed at the clinical centers. The patients will be provided with the usual clinical care given to all such patients at the respective centers. Baseline demographic information, selected laboratory tests, and other studies are being obtained at the initiation of the Continuation Study. The patients will be seen quarterly at the centers, and some selected studies done at these visits. Samples will be obtained and stored for additional studies and analyses at a later date.

The protocol used in the Continuation of AASK Cohort Study is similar to that proposed for the new Chronic Renal Insufficiency Cohort (CRIC) Study to be initiated by the middle to late 2002 to permit ultimate integration and comparison of the two data sets.