OrganOx Metra vs. TransMedics OCS

Medically reviewed by James F. Trotter, MD and Joseph S. Redman, MD, PhD, National Friends Medical Advisory Board · Last reviewed October 1, 2026

OrganOx metra and TransMedics OCS Liver both keep a donor liver warm outside the body. Here is how they differ and what to ask your team.

Both devices have FDA premarket approval for normothermic machine perfusion (NMP) of donor livers, and both are in clinical use in U.S. liver transplant programs. Both keep the donor liver warm and perfused with oxygenated blood between the donor operation and the transplant. They differ in how they were built, how they were tested, and what information they give the team during preservation.

What normothermic machine perfusion is

For decades, donor livers have been flushed with a cold solution and carried on ice. This is called static cold storage. It is simple and it works well for many livers, but the cold slows the liver down and the clock keeps running. Livers from older donors, or from donors after circulatory death (DCD), tolerate cold storage less well.

NMP takes a different approach. The liver is connected to a machine that pumps warm, oxygen-rich blood through it at close to body temperature. The liver keeps working: it uses oxygen and can make bile. That gives the surgical team two things cold storage cannot: more time, and a chance to watch how the liver is doing before they commit to the transplant. For the basics, see our plain-language guide to normothermic machine perfusion. For the cold-but-oxygenated alternative, see HOPE perfusion.

The two devices at a glance

OrganOx Metra

FDA approved the OrganOx metra System in December 2021 (PMA P200035). FDA describes it as a transportable device that keeps donor livers in a functioning state for a total preservation time of up to 12 hours, for livers from brain-death (DBD) or circulatory-death (DCD) donors.
It has the longer clinical track record overall. The first large randomized trial of liver NMP, published in Nature in 2018, was run at European centers using the metra.
Its U.S. pivotal trial (registered as NCT02775162) enrolled patients at 15 U.S. liver transplant centers.

TransMedics OCS

A multi-organ platform. FDA approved OCS Lung in 2018, and OCS Heart and OCS Liver in 2021. OCS Liver was approved in September 2021 (PMA P200031), a few months before the metra.
FDA describes OCS Liver as a portable system for preservation and monitoring of blood flow and metabolic function, which allows the team to assess the liver outside the body. It is approved for DBD and DCD livers.
Used by some programs that already have a heart or lung TransMedics workflow and want a single perfusion platform across organs.
Its U.S. pivotal trial, OCS Liver PROTECT, started perfusion at the donor hospital and enrolled 300 recipients at 20 U.S. programs.

What the clinical trials found

Each device was tested against cold storage, not against the other device. The trials used different patients, centers and goals, so their numbers cannot be lined up side by side to pick a "winner."

Metra in Europe (Nasralla, 2018). In 220 liver transplants, NMP-preserved livers showed about 50% less injury on blood tests, even though about 50% fewer offered livers were thrown away and livers were preserved about 54% longer on average. The trial found no significant difference in bile duct problems, liver survival or patient survival.
Metra in the U.S. (Chapman, 2023). 383 donor livers were randomized and 266 were transplanted. The main goal, fewer cases of early allograft dysfunction (a new liver that is slow to start working), was not met: 20.6% with NMP vs. 23.7% with cold storage. A sudden drop in blood pressure when blood flow returns to the new liver was less common with NMP (5.9% vs. 14.6%). The authors concluded that the biggest benefit seemed to be for higher-risk livers.
OCS Liver PROTECT (Markmann, 2022). Early allograft dysfunction was lower with OCS (18% vs. 31%). More DCD livers were used (51% vs. 26%). Bile duct injury caused by poor blood flow was lower at 6 months (1.3% vs. 8.5%).

All three trials were sponsored by the device makers, which is common for device approval studies.

How this affects a patient on the waiting list

Machine perfusion does not change your place on the list. Your priority still comes from your MELD score, blood type and distance from the donor hospital. What perfusion can change is how many offered livers your center feels safe accepting. A center that can test and use more DCD or older-donor livers may be able to say "yes" to an offer that another center would turn down. That is one reason the median MELD at transplant differs from center to center. Learn more about these donor types in DCD vs. brain death and extended-criteria donors.

What this means for caregivers

If your center uses NMP at all, that's the bigger signal. Trial evidence suggests machine perfusion can help teams use more livers, especially higher-risk ones, compared with cold storage alone. Asking which device they use is reasonable, but device choice is a smaller variable than program experience and case volume. You can compare programs on the interactive center map or browse the liver transplant centers directory.

Questions to ask your transplant team

Do you use machine perfusion for livers? If so, normothermic, hypothermic (HOPE), or both?
Which device or devices do you use, and who runs them? Some programs run perfusion with their own staff; others use an outside service.
How often do you accept DCD or older-donor livers? Ask whether perfusion has changed how often they say yes to offers.
Would you accept a perfused liver for me? Ask whether there is any reason, such as your diagnosis or other surgeries, that would change the answer.
How does your team decide a perfused liver is good enough to use? You don't need the technical details, just a sense that they have a clear process.

Common misconceptions

"A perfused liver is a lower-quality liver." Perfusion is often used to protect and test livers that might not do well on ice. In the trials above, outcomes for perfused livers were the same as or better than cold-stored livers on the measures studied.
"One device is proven better than the other." No trial has compared the two devices head to head. Each was compared with cold storage.
"Machine perfusion moves me up the list." It does not. It may increase how many offers your center can accept, but allocation rules stay the same.
"If my center doesn't use NMP, I should leave." Not necessarily. Many excellent outcomes come from cold-stored livers. Perfusion is one factor among many, alongside wait times, experience and what fits your situation.

Sources

Educational only. Not medical advice. Your transplant team has the final word.

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