One of the nation's most prominent medical centers has voluntarily suspended its living donor program for kidney transplants after a living donor died last month.

The donor had provided a kidney to a recipient at University of California San Francisco Medical center in October. Hospital and regulatory officials are still investigating the cause of death, the San Francisco Chronicle reported Saturday.

Dr. Steven Katznelson, medical director of California Pacific Medical Center's kidney transplantation program in San Francisco, called the donor's death a "nightmare scenario."

"We worry about it every day," he said. "For a healthy person who goes under general anesthesia, there's always a risk."

UCSF officials said the recipient's new kidney is working properly but they declined to identify the patient or the deceased donor. They wouldn't discuss the case further.

Most kidney transplant recipients receive kidneys from deceased donors, but those received from living donors generally have better outcomes. The risk of a kidney donor death following surgery is about three deaths in every 10,000 cases.

Four kidney donor deaths, including the one at UCSF, have been reported since 2014, according to the Organ Procurement and Transplant Network, which runs the United Network for Organ Sharing waiting list and oversees transplantation nationwide.

Hospital officials say UCSF has performed more kidney transplants overall than any other center in the country, with more than 10,000 since 1964. Doctors there performs about 350 kidney transplants a year, with about 150 involving living donors.

UCSF says that during the investigation it will not conduct the transplant surgeries on donors but it will continue transplanting kidneys from both living and deceased donors into recipients.

Physicians at California Pacific will take over the donor side for several transplant surgeries that are scheduled at UCSF before the new year.

"Our goal is to help (UCSF and its patients) as much as we can," Katznelson said.