The number of donor livers thrown away in the U.S. has increased since 2004 due - in part - to a population growing older and heavier, according to a new study that also points to changes in medical practice that may make some donor livers less viable.
"The rationale for looking at this question in the first place is that the number of liver transplants done in the U.S. has gone down," said the study's lead author Dr. Eric Orman, a fellow at the University of North Carolina at Chapel Hill.
To identify factors that might explain the trend, Orman and his colleagues used a national database of all organ donations beginning in late 1987 to see how many livers from donors of at least one organ were discarded, and why.
They found that the proportion of unused livers fell dramatically, from 66 percent in 1988 to 15 percent in 2004. After that, however, the percentage of unused livers began to rise again, hitting 21 percent in 2010.
Between 1988 and 2010, about 107,000 people donated their livers. Nearly 42,000 of those were after 2004. Of those post-2004 donations, about 33,900 livers were used and about 7,600 were not.
When the researchers, who published their results in the journal Liver Transplantation, looked at the differences between the livers that were used and those that weren't, they found a few possible links.
Specifically, livers from older, heavier and sicker patients were more likely to be thrown out between 2004 and 2010.
"That wasn't too surprising because a lot of those donors are more likely to have fatty livers. Those livers are avoided because they can lead to worse outcomes after transplant," said Orman.
And the proportion of older, heavier donors increased during the study period.
Between 1988 and 2010, the average donor age rose by almost 10 years, and the proportion of donors who were over age 50 grew from 16 percent to 38 percent. The proportion who were obese rose from 15 percent in 1995 to just over 30 percent in 2010. And donors with diabetes and high blood pressure grew from three percent in 1995 to almost 23 percent in 2010.
The findings suggest that overall population aging and rising obesity led to a decline in the quality of livers being harvested, and ultimately to an increase in the percentage of unused organs, the researchers write.
They also found that the number of livers donated after so-called cardiac deaths rose during the study period, and that those livers were more likely not to be used.
In traditional donations after brain death, the body's heart is still pumping and supplying blood to organs because it's still attached to life-support machines. In donation after cardiac death, those machines have been disconnected.
Because livers donated after cardiac death have sometimes been linked to worse outcomes after transplant compared to brain-death donations, the fact that more cardiac-death organs were discarded did not surprise the researchers.
They found that cardiac death livers made up a quarter of all unused livers by 2010, whereas in 1995 they were just one percent.
"The problem is that the standard (or brain death) donors seem to be decreasing over the last few years, and the number of (cardiac death) donors is increasing," said Orman.
One possible explanation, the researchers write, is that machines keeping the heart beating are being removed earlier, which would turn a potential brain death donation into a "less desirable" cardiac death donation. Though, there is no evidence to support this concern, Orman cautioned.
Orman told Reuters Health that one limitation of the new study is that he and his colleagues cannot say for certain why livers were discarded
"We couldn't look at the actual reasons, but we could look at associations," he said.
Dr. David Reich, professor and chief of transplantation at Drexel University and Hahnemann Hospital in Philadelphia, said he agrees that organ donors are older, sicker and more obese, but he does not think cardiac deaths are "cannibalizing" the supply of potential brain-death livers.
Rather, he told Reuters Health, brain deaths are declining because of the advancement of neurological techniques.
"The cardiac deaths are growing because of changes in management by neurologists and neurosurgeons," he said. "That's good for patients but it's going to cost us some donors."