Organ transplants in the United States reached an all-time high for the fourth consecutive year in 2016, according to the United Network for Organ Sharing (UNOS). Preliminary data from UNOS shows transplants increased 8.5 percent from 2015 and 19.8 percent since 2012, with doctors performing 33,606 transplants in 2016.

The increase in transplants is largely attributable to an expanding number of deceased donors. Living donors provided only 18 percent of organs for transplant. The remaining 82 percent of the transplants involved organs donated by deceased donors, who frequently provide multiple organs.

The rise in deceased donors is a direct result of loosening restrictions that would have prevented the individuals from donating an organ in the past. Many present-day donors have medical characteristics that would have precluded them from donating just a few years ago.

Donations now come from people who donated after circulatory death (as opposed to brain death), have an increased risk for blood-borne disease or have died of drug intoxication. In fact, a study published in the June 2016 issue of the Canadian Journal of Surgery found the characteristics and comorbidities of brain-dead donors has deteriorated significantly in the past decade, with an increasing number of donors presenting with increased body mass index (BMI), smoking history, coronary artery disease and dyslipidemia.

Dr. David Klassen, chief medical officer of UNOS, notes that there are currently no uniform criteria for donations or enforced guidelines within the existing network of organ procurement and donation. Instead, organ transplant professionals determine if a particular donated organ will be safe for an individual patient. The organ donation professional would decide if an elderly deceased person would be a suitable donor, for example, or if a particular organ would be the right fit for a certain child.

The rising death toll from the opioid epidemic sweeping the nation is also increasing the number of donor organs.

"The number of donors who died of overdoses increased over the past year," Klassen said. Nearly 25 percent of the donor population in some parts of the nation had died from opioid overdoses.

According to statistics presented by the American Society of Addiction Medicine, there were 20,101 overdose deaths related to prescription pain relievers in 2015 and 12,990 overdose deaths associated with heroin that year. While medical professionals and others are working hard to end opioid overdoses, the transplant community continues to make use of all potential donors.

UNOS is an organ-sharing network serving as the Organ Procurement and Transplantation Network (OPTN) working under contract with the U.S. Department of Health and Human Services, Health Resources and Services Administration, Division of Transplantation. Its purpose is to bring together medical professionals, donor families and transplant recipients.

The increase in donor organs is also the result of energetic work on the part of organizations, like Donate Life America, organ banks and community organizations that promote the donation of organs.

Some organ donation organizations work closely with motor vehicle departments to make it faster and easier for people to register as organ and tissue donors when they get or renew a license, for example. Other efforts provide support and information to help families of recently deceased unregistered individuals make decisions about organ donation.

With 19,057 transplants in 2016, kidneys are the most commonly requested and transplanted organ each year. This is due, at least in part, to the effectiveness of dialysis in prolonging the life of people waiting for a kidney transplant. There were 7,841 liver transplants, 3,191 heart transplants and 2,327 lung transplants in 2016.

About 119,053 people in the United States are currently waiting for a life-saving organ.