It’s a medical mystery: Why are most people born with two kidneys when it is possible to live a full, healthy life with only one of these blood-filtering organs?

“Nobody knows why most people are born with two kidneys when we really only need one,” says Christina Klein, M.D., a transplant nephrologist at Piedmont Transplant Institute.

Dr. Klein says she likes to use percentages when describing normal kidney function in different patient groups:

• People born with both kidneys: 100%

• People born with only one kidney: 75%

  • “Before they were born, [a person with only one kidney] developed more kidney tissue than you would have expected with just one kidney,” Dr. Klein explains.

• Patients who had a kidney removed for health reasons or organ donation: Initially 50% post-surgery, but increases to 75% over time.

  • Studies show that when someone donates a kidney or has one surgically removed, their initial function post-surgery is 50%. However, over time, thanks to a hyperfiltration process and tissue growth, function increases to 75%.

Living kidney donation

“When we counsel people who are interested in donating a kidney, we stress to them the importance of a healthy lifestyle long-term to preserve the function of the kidney they have left,” she says.

People interested in donating a kidney must go through a rigorous screening process for pre-existing kidney disease and risk factors for future kidney disease.

Dr. Klein recommends the following for patients to maximize their health with only one kidney:

• Maintain a healthy weight

• Get regular exercise

• Follow a nutritious diet low in salt and fat

Life after living kidney donation

“I don’t understand why people are born with two kidneys, but I’m very grateful we are able to live with one kidney because it not only enables us to do kidney transplants successfully, but it also enables us to do kidney transplants from living donors,” Dr. Klein says.

It is possible to donate a kidney to someone else, and most donors do not have to worry about long-term health consequences.

“We know that someone who passes the donor screening and is able to donate a kidney to a loved one can live a nice, healthy, long life with just one remaining kidney,” she says.

To learn more about living kidney donation, visit Piedmont Transplant Institute. 

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