Treating elevated blood pressure can halt -- and even repair - kidney damage caused by the disorder, according to a new analysis of a large study. However, the renal benefits of lowering blood pressure extend only to nonblacks: For as-yet-unknown reasons, blacks with hypertension tend to go on to develop kidney damage whether they receive treatment for the disorder or not, the study found.
The results represent the first time researchers have proved that mild hypertension -- defined as blood pressure between 140/90 millimeters of mercury (mm Hg) and 159/99 mm Hg -- or moderate hypertension -- between 160/100 mm Hg and 179/109 mm Hg -- in fact impairs kidney function. Previous studies only suggested a link between kidney damage and blood pressures in either of these two ranges, which physicians now refer to as stage 1 and stage 2 hypertension, respectively (SN: 11/7/92, p.311).
Kidney dialysis centers estimate that the renal failure of roughly one-third of all new dialysis patients derives from damage caused by hypertension. Besides serverely curtailing patients' lives, these new dialysis cases add approximately $300 million per year to already spiraling U.S. health care costs, according to the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Md.
To confirm the hypertension-kidney damage connection, a research team led by W. Gordon Walker of Johns Hopkins University School of Medicine in Baltimore measured concentrations of a waste protein called creatinine in the blood of 5.524 hypertensive men of all races. Because the kidneys usually filter creatinine -- a by-product of normal metabolism -- out of the blood and into the urine, blood creatinine measurements can indicate whether a patient's kidneys are working properly.
The men studied by Walker's group were a subset of participants in the Multiple Risk Factor Intervention Trial (MRFIT), an even larger study evaluating measures to prevent heart disease among men at risk for the disorder because of cigarette smoking, elevated blood cholesterol, or elevated blood pressure. As part of the MRFIT design, roughly half of the men were given a standardized regimen of drug therapy and put on a modified diet to control their blood pressure. The other half received a variety of different drugs and diet advice from their own physicians.
Walker's group found that the same treatments effectively controlled blood pressure among both blacks and non-blacks, most of whom were white. …