Lomu was diagnosed with a debilitating kidney disorder in 1995, a year after his All Black debut, and was donated a new kidney in 2004.
Professor Munn said some kidneys transplanted more than 40 years ago in New Zealand continued to function: "We have people who were transplanted right back in the 1970s who still have kidneys going now."
He said there were "literally a hundred different reasons" why Lomu's transplanted kidney might have failed, including infection, rejection, and mechanical problems within the new organ.
Reviving the kidney was always the first choice for doctors. But if Lomu's kidney could not be saved, he would be placed back on a waiting list for a new transplant.
New Zealand's deceased donor waiting list has about 600 people on it, with an average wait time of three years. The rarer the person's blood type, the longer the wait.
But like Lomu's first donated kidney, many transplanted organs came from friends or family.
Auckland renal specialist John Rosman said: "The waiting list is a rough estimate because there are people who wait only six months for a kidney.
"But if they have a more difficult blood type then they have to wait for a kidney for, maybe, eight years.
In order to work around that, 50 per cent of all the [transplanted] kidneys in New Zealand are from living donors."
People who had a second transplant faced new complications as the body had to re-adjust to another foreign organ. They must also repeat the extensive health and psychological checks to qualify for a donation.
If Lomu loses his kidney, the All Black hero is unlikely to be short of offers for a new one. His wife, Nadene, immediately offered one of her own, if compatible, and numerous Herald readers responded to yesterday's story by pledging theirs to the Tongan giant.
