African Americans under age 50 face higher risks of dying while on kidney dialysis than their white counterparts, said a US study published Tuesday that contradicts previous research on the topic. Researchers at Johns Hopkins University described their findings as "surprising," and suggested that doctors should advise young blacks differently than whites about the risks of undergoing the blood-filtering procedure. The study in the Journal of the American Medical Association examined 1.3 million patients with end-stage kidney disease and showed that blacks age 18-30 were twice as likely to die as their white counterparts. Blacks age 31-40 were at about 1.5 times higher risk of dying than whites. "As a medical community, we have been advising young black patients of treatment options for kidney failure based on the notion that they do better on dialysis than their white counterparts," said lead author Dorry Segev of Johns Hopkins. "This new study shows that, actually, young blacks have a substantially higher risk of dying on dialysis, and we should instead be counseling them based on this surprising new evidence." The differences could come down to economic disparities -- young blacks are less likely to have health insurance coverage than whites, so they may get less regular treatment and may be less able to pay for kidney transplants. They could also be rooted in physiological causes such as hypertension which is more prevalent in blacks. Or fewer blacks may be referred for kidney transplants because of the widely held belief that they do better than whites on dialysis, said Segev, who is a transplant surgeon. Study co-author Lauren Kucirka, also of Johns Hopkins, said: "The next important step is to try to figure out why there is such a high relative risk of death for young black patients on dialysis." As many as 30 previous studies have shown that black patients on dialysis survive longer than whites, and have a 13-45 percent lower mortality rate. The JAMA study analyzed data from more than 1.3 million patients and said disparities turned up when the records were grouped according to age, showing a small benefit for older blacks on dialysis but much higher risks for younger blacks. "We have shown that the commonly cited survival advantage for black patients undergoing dialysis applies only to those older than 50 years of age," it said. Most people who undergo dialysis are over 65. In the United States some 500,000 people have end stage renal disease, which requires either a kidney transplant or dialysis several times per week to remove waste and excess water from the blood.