“The past week was important. Without my liver to extend Tang’s life, she would not have been able to wait for one from a deceased donor,” she replied when asked how she felt about the second transplant.

“I think it was worthwhile to use my 0.5 per cent mortality rate [as a liver donor] in exchange for Tang’s 90 per cent survival rate.

“I felt saving a life came first ... but I did struggle as my mother also has a liver problem, and I can donate my liver only once in my lifetime.”

Cheng was discharged from hospital on Thursday night following a satisfactory recovery.

Professor Lo defended the first operation, insisting it was “never a failure” and the effort was not wasted. But Cheng’s liver, removed from Tang’s body, could not be reused by another patient as it was already damaged due to blood loss.

“It was never a failure, it extended Ms Tang’s life for seven days, allowing her to wait for another donation,” the doctor said on Friday.

“The donation made by Ms Cheng saved her life. Without it, there was an 80 to 90 per cent chance she would not make it.

“I also believe her generous act may have encouraged the family of the deceased patient to agree to the organ donation. It had a positive effect on society.”

Lo expressed hope Tang would regain enough liver function to no longer require breathing machines and peritoneal dialysis, as these could increase chances of complications. Professor Yuen Kwok-yung, the University of Hong Kong’s top microbiologist, was helping the team to minimise Tang’s risk of infection.

Since the 1990s, Queen Mary Hospital has handled 57 cases that required a second liver transplant. Such cases accounted for around 4.4 per cent of all the hospital’s liver transplant cases, according to Dr Kelvin Ng Kwok-chai, another expert from the department of surgery.

He said the five-year survival rate for local patients who had a second liver transplant was 85 per cent – higher than the international rate of around 70 per cent.