BEND (AP) — Greg Sabin isn't afraid to admit it. He's not exactly the most patient person. So when his doctor told him it'd be at least six weeks after he donated a kidney before he could crank up his workout routine to its usual intensity, he wasn't thrilled.

"I want to be good as gold straight out of the gate," said the 56-year-old Bend resident. "I never really had surgery before, so I didn't really know what to expect."

Sabin didn't swim for a while. He kept his runs short and not too fast. Then, exactly five months after the surgery, he completed a triathlon in Sunriver: a 1.2-mile swim, 58-mile bike ride and 13-mile run.

"It was like a holiday for me," he said of finally getting back into intense exercise.

In January, Sabin donated one of his kidneys to his wife, Stacey, who has a genetic condition called polycystic kidney disease. It causes water-filled cysts to crowd the kidneys and liver, eventually impairing their function. Both of their recoveries have gone smoothly.

Now that Sabin is back in his normal routine — not to mention training for another triathlon — he hopes his experience can be a lesson for others who are hesitant about kidney donation, perhaps fearing it will hamper their athletic performance.

"There was never even a second that I thought that I would accept being less active than I was before," he said, "and I still won't."

Transplant specialists say there's no reason living kidney donors can't continue being competitive athletes, including running in marathons or even ultramarathons.

Dr. Charles Modlin, a kidney transplant surgeon with the Cleveland Clinic, said that's an important message to get out, as living donors are crucial. Not only are there not enough kidneys to go around from deceased donors, transplants from living donors typically have the best outcomes.

"There are a lot of misconceptions that if you donate a kidney, you can't live out your life normally, and you're going to be infirm," Modlin said. "That's just not the case."

'Drink to thirst'

There are, however, important caveats to consider.

Dr. Kayvan Roayaie, an assistant professor of surgery in the division of abdominal organ transplantation at Oregon Health & Science University, said after someone donates a kidney, it's "critically important" to preserve their remaining kidney function.

That means if people plan to engage in intense exercise, they should make sure they're staying hydrated and allowing time for their incisions to heal. Roayaie, who removed Sabin's kidney, said he typically counsels people to wait at least six weeks before vigorous exercise to allow the scar over the abdominal wall — where the surgeon enters to remove the kidney — to develop adequate scar tissue.

Working those muscles too hard before the incision heals enough can lead to hernias, which is when an organ pushes through an opening in the muscle that holds it in place. Abdominal hernias are the most common type.

Sabin said he's noticed he's had to drink more water after the surgery compared with before to avoid cramping during exercise. He also drinks more water over the course of a normal day.

Doctors interviewed for this article said they don't necessarily recommend kidney donors increase their water intake beyond normal, unless they were dehydrated before the surgery. In follow-up exams, Roayaie said doctors will check the moisture of donors' mucous membranes and the turgor of their skin.

After someone donates a kidney, the remaining kidney actually enlarges to compensate and provides between 70 to 80 percent of the total function both kidneys previously contributed together, Modlin said.

"So they don't have to drink an excessive amount of fluid," he said. "Just drink to thirst."

'Extreme stress on the body'

One of the big differences Sabin said he noticed between the triathlon he performed in June and previous races was his energy level wasn't as high as it used to be. As a result, his time was slower than he would have liked.

Fatigue is almost a universal experience for kidney donors, Roayaie said. Typically, they're back to their usual energy levels about a month after the surgery.

"Surgery, even for a healthy person, is an extreme stress on the body," Roayaie said. "The body is pouring a lot of that energy into healing and creating new scar tissue, and that all of that contributes to the fatigue."

As far as completing a triathlon five months after the surgery, Roayaie said he's not surprised Sabin noticed the effects. There are still changes happening in the body within the first year after donation, he said.

It takes four to eight months for the remaining kidney to enlarge to compensate for the missing one, so it's possible that put a damper on Sabin's performance, Modlin said. It could also be he wasn't able to train as hard as he usually does, he said.

"It's remarkable that he was able to do it," Modlin said.

OHSU performs extensive testing on living donor candidates to ensure their bodies can handle the shock. Diabetes and hypertension are the most common conditions that disqualify people from donating, Roayaie said.

Before he was approved to donate, Sabin said doctors were alarmed by his scores on some of their tests. When his heart rate came up as 43, for example, they suspected a heart condition. He was able to convince them that's just his normal resting heart rate.

"They didn't know what to do with it," he said.

Risk low, but not zero

While extensive research has been done on how transplant recipients fare after getting a new kidney, less is known about living donors.

The United Network for Organ Sharing, a nonprofit organization that manages the nation's organ transplant system through a contract with the federal government, requires all transplant centers, like those at OHSU and Cleveland Clinic, for example — to follow up with living organ donors for at least two years. Hospitals are required to send UNOS data on donors' kidney function and whether they had any hospitalizations, organ failures or deaths. Providing the information is voluntary on the patient end.

The risk to donors is low, but it's not zero, said Dr. David Klassen, UNOS' chief medical officer. In the same way as getting one's appendix removed, there's always a small risk of death. For kidney donors, the risk of death is about three in 10,000 people, he said. Another roughly 30 in 10,000 people develop kidney failure after donating a kidney.

"That's fairly small," said Klassen, also a nephrologist. "But again, there have been lots of living donors over the years. To the extent we've been successful in collecting that information, we have a fairly solid understanding of what the risks are."

A partner organization to UNOS, the Scientific Registry of Transplant Recipients, is creating a living donor registry in hopes of tracking donors longterm.

'You can still participate'

For her part, Stacey Sabin said with a laugh that getting her husband's kidney hasn't motivated her to get out and do a triathlon. Her goal for 2018 is to exercise more.

"I live with an Ironman, so I hear it all the time," she said, referring to the Ironman competitions her husband has participated in.

Insomnia is one of the side effects of the medications she takes to prevent her body from rejecting the kidney, so gathering the energy to exercise has been a challenge. She relies on Facebook groups and other online networks to learn about other people's post-transplant experiences. She's been relieved to learn her side effects are normal.

As for her husband, he's in the throes of training for a half-Ironman competition in St. George, Utah, in May, the same one he did in 2014. His goal is to match his 2014 time. The paved course, which features steep hills carved into the red rock canyon, is the toughest he's ever done.

"I'd like to bring awareness to the fact that you can still participate — and hopefully somewhat competitively — in this stuff after such a thing," he said.

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