It pays for 80 percent of dialysis costs, which are about $48,000 a year. It generally funds more than that proportion of transplant costs, which average $92,000.

For about a decade, studies have found racial discrepancies in the treatment of kidney failure, heart disease, arthritis, cancer and other life-threatening illnesses.

The HMS study found that several of the reasons usually offered for the racial gap do not account for the difference. Three common theories are that more black patients do not want transplants, that fewer black patients have private health insurance and that more black patients have fatal diseases that make transplants unnecessary.

However, the HMS study found that three-fifths of the racial gap remained after taking all of those factors into account.

Ayanian, who also works at Brigham and Women's Hospital, said he believes results would be similar for other conditions such as heart disease.

The HMS researchers looked at kidney transplants in part because the HCFA's program makes money less of an issue for patients who do not have their own insurance, Ayanian said.

The study was published Nov. 25 in the New England Journal of Medicine.