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A student and staff watch over a donor during a kidney transplant at Johns Hopkins Hospital, June 26, 2012, in Baltimore. A donor in San Francisco died recently after donating a kidney. AFP/GettyImages/Brendan Smialowski

One of the U.S.'s well-known medical centers has voluntarily suspended its living-donor program for kidney transplants following the death of a patient last month. The donor had provided a kidney in October to a recipient at the University of California San Francisco Medical Center, the Associated Press reported Sunday.

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

"We worry about it every day," Katznelson said, according to the Associated Press. "For a healthy person who goes under general anesthesia, there's always a risk."

The cause of death is being investigated by hospital and regulatory officials,the San Francisco Chronicle reported Saturday. The transplant-receiving patient's kidney is functioning properly, according to hospital officials, who declined to identify the deceased donor or the recipient, the Chronicle reported.

The risk of kidney donor death after surgery is some .03 percent, or about three deaths per 10,000 cases. Most kidneys used in transplants come from deceased donors, but kidney donations involving living donors typically have better outcomes. A living donor typically gives away a kidney as a kind act for a friend or family member.

Two kidney donors have died at United States transplant centers this year, and two died in 2014, according to the Organ Procurement and Transplant Network, a national organization, the Chronicle reported. The University of California San Francisco Medical Center has performed more kidney transplants overall than any center in the country, with more than 10,000 since 1964. It performs some 350 such transplants annually, about 150 of which involve living donors.

Physicians at California Pacific said they were scheduled to take over the donor side for a number of transplants that are scheduled before the year's end. “Our goal is to help [UCSF and its patients] as much as we can,” Katznelson said to the Chronicle.