The U of M study is the largest, and one of the longest retrospective studies to date, looking at the risks of kidney donation.
Researchers examined the outcomes of nearly 3,700 people who donated a kidney at the U of M. They tracked donors all the way back to 1963.
Out of the 3,700 donors, only 11 people went on to develop kidney failure requiring dialysis or kidney transplantation, according to principal investigator Dr. Hassan Ibrahim.
"And that risk of kidney failure is much lower than what is generally observed in the general population," Ibrahim said. "So we're really assured -- not only do they live as long, if not longer than the general population, but the risk of kidney failure is not increased."
"Not only do [kidney donors] live as long, if not longer than the general population, but the risk of kidney failure is not increased."
Donors must pass strict selection criteria before they're allowed to donate a kidney. Donors can't have diabetes, hypertension or be obese. The good health of the donor population proves that those restrictions have paid off, Ibrahim says. That should be comforting to anyone considering kidney donation.
"That would be the true reward from this work," Ibrahim said. "We're hoping it will get people more interested in living donation, because we currently have over 100,000 people on the kidney transplant list. And roughly 10 percent of these people die per year waiting for a kidney transplant."
In 1967, Tony Thein gave one of his kidneys to his younger brother Tom. Both men were in their mid 20s at the time. Tony Thein is now 70.
"It certainly has never slowed me down," he said.
The only consequence of his surgery is a small scar on the side of his back, Thein said. He wants everyone to know that he has never had any problems living with one kidney.
"If those of us who have done it over this long period of time have survived this well, I'd like to be the model for others who might say, 'Gee, I've considered it, but I'm not sure I want to go forward with it,'" Thein said.
His brother Tom is doing well, too. He turns 69 in May, and is still married to the nurse he met while recovering from his transplant.
But like any study, the U of M's findings have limitations.
The population in the U of M study does not reflect the ethnic composition of the U.S. population, said Dr. Jane Tan, a kidney specialist at Stanford University, who reviewed the research and published a companion editorial in the New England Journal of Medicine.
"It is a predominantly white population, and whether this also applies to other ethnicities, specifically African American and Hispanic -- we presume that it is, but we don't fully know," Tan said.
For example, African Americans have a much higher rate of diabetes, hypertension and end stage kidney disease than Caucasians. So it's possible they might be more likely to develop those conditions after donating a kidney.
Tan also wonders about older donors. Every year the average age of living donors increases, she said. Some people who donated 40 years ago might have been in better overall health than people who donated just 10 years ago, she said, and that could skew the results of the study.
But overall, she concludes the U of M study is well-designed and its conclusion seems solid.
"I think with this study we can more safely say that, indeed, living kidney donors screened in the way that the authors mentioned do not have undue harm in the future," Tan said.
The U of M is in the process of expanding its research to other regions of the country. They hope a more geographically diverse study of kidney donors will help them answer any remaining questions.
The study was funded by the National Institutes of Health, the General Clinical Research Centers and the Monica Libin Fund.