A racial gap in kidney transplants appears to have closed, a 13-year study found.

Rates of such transplants among white patients used to far surpass those in blacks, but U.S. data on nearly 200,000 end-stage kidney disease patients shows that disparity had disappeared by 2010. Rates remained stable in 2011 and that trend likely has continued, said Dr. Jesse Sammon, the senior author and a urologist-researcher at the Henry Ford Health System in Detroit.

The rate among black patients climbed from 93 per 1,000 patients in 1998 to about 128 per 1,000 patients in 2010 and 2011. That was also the 2010-11 rate for whites, a slight decline from 1998.

The trend among blacks was "driven wholly by increased rates of transplants from deceased donors," the study authors said. About 80 percent of operations in blacks in 2011 were cadaver organs, which tend to fare worse than those from living donors.

So while the study is mostly "good news," more work is needed to eliminate racial disparities among kidney transplant recipients, Sammon said.

The study was published Monday in JAMA Internal Medicine.

"This is what we've been working for years, to make sure we have equitable access to every potential candidate across the United States," said Dr. Mark Aeder, chairman of the United Network for Organ Sharing' kidney committee. He was not involved in the research.

The trend likely stems from a 2003 change in a national allocation policy for donor kidneys which eased a restriction on certain partially matched donor kidneys. Transplants have the best chance of success when donor organs contain certain proteins that completely match those of the recipient. Perfect matches are most likely when donors and recipients are the same race, but transplants involving partial matches also can work.

With improvements in transplant techniques and in drugs to prevent transplanted organs from being rejected, recipients of partially matched organs can fare well, Aeder said.

A new matching system that took effect last December was designed in part to further improve rates among African Americans. Its features include counting waiting time for a kidney from the date patients start dialysis, rather than when they joined the transplant list. Transplants generally go to those who've waited the longest.

End-stage kidney disease is more common in blacks, and they comprise about one-third of patients on the national waiting list for kidney transplant.

Dr. Dorry Segev, an organ transplant specialist at Johns Hopkins University, noted that younger blacks on dialysis die at nearly twice the rate of whites and are less likely to be referred for a transplant. Still, he said it's encouraging that once on the list, "they receive fair organ allocation and achieve good transplant outcomes."