Waterford — When 61-year-old East Lyme postal worker John Guarino goes to the hospital Thursday for a kidney transplant operation, he will be expecting a small gift from his wife, Diana.

The gift of life.

That's because Diana, the woman he has been married to for 37 years and had two children with, will be his kidney donor.

The two met in high school back in the late 1970s and have been inseparable ever since. But when John's kidneys began to fail it seemed unlikely that Diana would be a match, since she comes largely from Irish stock while John's background is Italian.

"We had zero idea I would ever be a match," Diana said in an interview last month at their Quaker Hill home.

Yet when Yale New Haven Hospital did a tissue analysis, doctors found the two were compatible, which was a good thing because otherwise the wait for a live donor could have been years — and John's kidneys were failing fast. They have since been removed altogether.

After the match was confirmed, Diana then had to undergo a nine-hour battery of psychological tests to determine if she was mentally prepared for the operation and recovery period. Doctors also wanted to be sure she wasn't being coerced into making the donation against her will.

"It was nerve racking because I really wanted to be the donor," Diana said.

But there was another problem as well. John had been born with a heart murmur, and he was now having heart issues that doctors were afraid could preclude him from being a good candidate for the transplant.

"We're not going to give you a kidney and have you have a heart attack," John recalled the doctors saying.

So about seven months ago, John underwent a successful eight-hour heart surgery.

"It was super scary," Diana said.

And John's family history didn't make the situation any less scary. His father, Ray Guarino, had died in his early 40s because of the same inherited condition called polycystic kidney disease that leads to cysts forming on the kidney.

"On X-rays, the kidneys look like shattered glass," he said.

John remembers his dad doing dialysis at his Waterford home while he was a teenager, the first in the area to do so, but he never got a kidney transplant.

"This gives me the best life expectancy," John said of the transplant. "I wanted to do it now. I'm only getting older."

The kidney condition has sapped John's energy level for many years, though he continued to sort and deliver mail at the East Lyme post office. Diana said the work took a lot out of him, and he spent much of his time at home resting in recent years.

John started his postal career about 15 years ago at the tiny office in Quaker Hill, a place he could walk to from his home. Later, he transferred to East Lyme, where he worked for several years until last July, when his kidney function dipped below 10% and it became too difficult.

It then became imperative to get a kidney transplant, but he quickly found there was a four- to six-year wait for people with his blood type, A negative. He started searching for a donor, reaching out to friends and acquaintances, unaware his best match had been standing beside him all along.

The Guarinos' 29-year-old son Peter, an aeronautics engineer, was also a likely match, but the couple didn't like the idea of him going through an operation at this stage of his life.

"We preferred Pete not to be the donor," Diana said. "He's a new dad."

And 27-year-old son James, though currently undiagnosed, has exhibited signs that he may have inherited the gene that makes it a 50-50 possibility a Guarino offspring would develop polycystic kidney disease, she added.

John said one of his brothers also is suffering with the disease. The Guarinos said they were sharing their story in the hope that it would inspire more people to consider organ donation.

The operation John and Diana are about to undergo usually lasts about eight to nine hours, they said. It is officially known as a "paired donation," meaning two people are donating kidneys at the same time and aren't supposed to know whether their organ will end up in a loved one or a stranger.

"They're just going for the best match," Diana said.

"I'm not supposed to know she's my donor," John added.

Diana will likely be released the day after the operation, but will require weeks of recuperation. She's had to tell clients of her day care services that they will need to make other arrangements for a while.

John, meanwhile, will require two to three days at the hospital to recuperate. And he will likely need a little more time than Diana to be back to work at the post office, where he hopes to be able to retire in five years.

"He's a good a patient ... he's a good healer," Diana said.

They'll have help from family and friends, they said, including one neighbor who already has been pitching in by mowing the lawn.

John is looking forward to having more energy, staying awake for a movie and perhaps going back to fishing with his friends. But he's already told them he can't go out drinking with them anymore. Alcohol can be a factor in a kidney being rejected, he said.

"I'm going to do everything I can to help this kidney," John said.

l.howard@theday.com