People who donate a kidney to a sick friend or relative live at least as long as others in the general population and may live somewhat longer because they tend to take better care of themselves after the procedure, researchers reported Tuesday.

“We have intuitively . . . felt this way, and hoped that this operation is safe, but this is the first time that we have been able to demonstrate it in a national representation of live donors,” said Dr. Dorry L. Segev of the Johns Hopkins School of Medicine, lead author of the report in the Journal of the American Medical Assn.

Live-donor transplants have become increasingly common in recent years because of the large number of people who need kidneys and the limited availability of cadaver organs.

There are 83,754 Americans waiting for a kidney transplant, 80% of the number of people waiting for any organ, according to the United Network for Organ Sharing, which helps allocate organs. In 2008, there were 5,968 living-donor kidney transplants.

Several small studies have suggested that donation is safe, but the low rate of risk has made accurate estimates difficult. To surmount that problem, Segev and his colleagues studied the 80,347 Americans who donated kidneys between April 1, 1994, and March 31, 2009. The team compared them with 9,364 participants in a large government survey -- the third National Health and Nutrition Examination Survey -- who met the criteria for kidney donation.

There were 25 deaths in the first 90 days after surgery among the donors, for a rate of 3.1 deaths per 10,000 subjects, compared with a rate of 0.4 per 10,000 in the control group. That suggests the procedure “has always been profoundly safe,” Segev said.

Death rates in the first 90 days were slightly higher for men than for women and for blacks than for whites. The highest risk, 36.7 deaths per 10,000 donors, occurred among donors who had high blood pressure.

From the survey forms used in the study, it is not clear if the hypertension was controlled or uncontrolled, Segev said. But it “would probably be wise for hypertensive patients considering donation to be treated through a carefully maintained protocol,” he added.

The results “confirm that this is a safe operation,” he said. “But it also gives us more specific numbers that we can give patients who are considering doing this. This is a very personal decision with no medical benefit for the donor, so it requires very careful consideration of what the risks are.”

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