In the US, a new patient is added to the waiting list for an organ transplant every 10 minutes.
With an opt-in system, people have to actively sign up to a register to donate their organs after death. In opt-out systems, organ donation will occur automatically unless a specific request is made before death for organs not to be taken.
Prof. Eamonn Ferguson, lead author from the University of Nottingham, UK, acknowledges that because the two systems are reliant on an active decision from individuals, it can lead to drawbacks:
"People may not act for numerous reasons, including loss aversion, effort, and believing that the policy makers have made the 'right' decision and one that they believe in."
However, inaction in an opt-in system can lead to individuals who would want to be a donor not donating (a false negative). In contrast, inaction in an opt-out system can potentially lead to an individual that does not want to donate becoming a donor (a false positive).
The US currently uses an opt-in system. According to the US Department of Health & Human Services, 28,000 transplants were made possible last year due to organ donors. Around 79 people receive organ transplants every day. Unfortunately, around 18 people die every day, unable to have surgery due to a shortage of donated organs.
In or out?
Researchers from the University of Nottingham, University of Stirling and Northumbria University in the UK analyzed the organ donation systems of 48 countries for a period of 13 years - 23 using an opt-in system and 25 using an opt-out system.
The study authors measured overall donor numbers, numbers of transplant per organ and the total number of kidneys and livers transplanted from both deceased and living donors.
They found that countries using opt-out systems of organ donation had higher total numbers of kidneys donated - the organ that the majority of people on organ transplant lists are waiting for. Opt-out systems also had the greater overall number of organ transplants.
Opt-in systems did, however, have a higher rate of kidney donations from living donors. The apparent influence that policy had on living donation rates "has not been reported before," says Prof. Ferguson, "and is a subtlety that needs to be highlighted and considered."
The authors acknowledge that their study was limited by not distinguishing between different degrees of opt-out legislation, with some countries requiring permission from next-of-kin for organs to be donated. The observational nature of the study means that other factors that may influence organ donation remained unassessed.
The researchers state that their results, published in BMC Medicine, show that "opt-out consent may lead to an increase in deceased donation but a reduction in living donation rates. Opt-out consent is also associated with an increase in the total number of livers and kidneys transplanted."
They suggest that although the results could be used in the future to inform decisions on policy, they could be strengthened further through the routine collection of international organ donation information - consent type, procurement procedures and hospital bed availability, for example - which should then be made publicly available.
Prof. Ferguson suggests that future studies could also analyze the opinions of those who have to make the decision to opt in or opt out:
"Further research outside of this country-level epidemiological approach would be to examine issues from the perspective of the individual in term of beliefs, wishes and attitudes, using a mixture of survey and experimental methods."
"By combining these different research methods researchers can develop a greater understanding of the influence of consent legislation on organ donation and transplantation rates," he says.
The authors note that countries using opt-out consent still experience organ donor shortages. Completely changing the system of consent is, therefore, unlikely to solve such a problem. They suggest that consent legislation or adopting aspects of the "Spanish Model" could be ways to improve donor rates.
Spain currently has the highest organ donation rate in the world. The Spanish utilize opt-out consent, but their success is credited by experts to measures such as a transplant co-ordination network that works both locally and nationally, and improving the quality of public information available about organ donation.
Recently, Medical News Today ran a spotlight feature on whether animal organs should be farmed for human transplants. Could this be a solution to the organ shortage, or this a problem to be addressed through changes to organ donation policy?
Written by James McIntosh
Her father, Allan Turner, who is chief executive of Zaidee's Rainbow Foundation, said moving to an opt-out, or presumed consent, system would spur Australians to have conversations with their families about their organs.
An opt-out system could be expected to lift the organ donation rate by 20 per cent in the first few years, based on the experiences of countries such as Singapore, Austria and Belgium.
"We want to break the myth that it's a scary thing to donate, and if a seven-year-old girl can do it, anyone can," Mr Turner said.
Currently Australians need to record their intent to donate with the Australian Organ Donor Register, but their family can still overturn those wishes after their death.
A systematic review published in BMJ in 2009 found countries that introduced presumed consent systems lifted their organ donation rates within a few years.
In Austria, the rate increased from 4.6 donors per million people per year to 10.1 per million.
Kidney donation in Belgium increased from 18.9 to 41.3, while in Singapore it increased from 3.7 to 31.3.
But the researchers warned there may have been other factors affecting donation rates.
The Organ and Tissue Authority said it had no plans to introduce an opt-out system, and independent reviews in NSW, Queensland, Western Australia and Tasmania all decided against changing the consent arrangements.
International experience showed that the key to increasing donation rates was identifying potential donors within the hospital system, a spokeswoman said.
"The informed consent model used in Australia is an ethical and transparent approach which balances the need for organ and tissue donors with the right of Australians to make an informed choice," she said.
A web tool constructed by University of Sydney researcher Aric Bendorf shows the majority of countries with presumed consent laws have higher donation rates, but some of those countries also have very low rates.
"Alluring as it may be to believe that adopting presumed consent legislation will raise a country's donation rates, this is not an accurate assumption," the site warns.
The low organ donation rate in Australia is a touchy political issue.
The donation rate in Australia is 16.1 donors per million population, up from 12.1 million before the Organ and Tissue Authority was established in 2009.
But it has not improved as quickly as some had hoped.
University of Queensland research assistant William Isdale, who recommended that Australia move to an opt-out system in an article published in the Monash Bioethics Review in July, said an opt-out system would need to be complemented by other measures.
"Unless it's a very hard opt-out system there's still the chance that families can veto requests, but it changes what's expected or normal in society," Mr Isdale said.