NEW YORK (Reuters) -- Blacks with early kidney disease are about five times more likely than whites to develop end-stage renal disease (ESRD), a severe form that requires dialysis or kidney transplantation, new research shows.

In the U.S., ESRD is more common among blacks than whites. The current findings suggest that this difference is due not to early disease being more common among blacks but rather from a higher risk of progressing to ESRD in blacks. "Black Americans make up a third of the dialysis population, but only about a tenth of the overall population," lead author Dr. Chi-yuan Hsu, from the University of California at San Francisco, said in a statement. "But nobody has ever looked at whether blacks have more early kidney disease than whites."

To better understand the racial difference in ESRD, Hsu's team analyzed data from the Third National Health and Nutrition Examination Survey and the U.S. Renal Data System.

The new findings are reported in the Journal of the American Society of Nephrology.

The authors found that the number of early kidney disease cases per 100,000 people in the population was not much different for each ethnic group -- 2060 for blacks and 2520 for whites.

In contrast, the risk of disease progression did differ markedly between the groups.

For every 100 blacks with early disease in 1991, five would develop ESRD by 1996. In contrast, among whites, only one patient with early disease would have developed ESRD during this period. Moreover, this link remained strong even after accounting for other known ESRD risk factors, such as age and diabetes.

Exactly why blacks with early disease are more likely to progress to ESRD than their white counterparts is unclear. However, the authors did find that blacks with early disease had higher blood pressures than whites.

Still, this difference is unlikely to completely explain the higher risk of disease progression seen in blacks, Hsu notes. Quality of care and access to health care issues could also play a role, he adds.