Plain language summaries of research

This is a plain language summary of an original research article. The views expressed are those of the author(s) and reviewers(s) at the time of publication.

Why do kidneys need to be preserved?

For people with kidney failure, a kidney transplant can give them a much better quality of life compared to staying on dialysis (a treatment that replaces the function of the kidneys by removing waste and excess fluid from the blood). However, there are not enough donated kidneys for everyone who needs one. Preserving donated kidneys while they are outside the body before they reach the recipient can help the chances of having a successful transplant and increase the number of suitable kidneys available.

 

How are kidneys currently preserved?

Currently, kidneys from donors are usually kept cold on ice before they are transplanted to someone with kidney failure. This method slows down damage that happens to the kidney while it is outside the body, however, it does not stop it completely.

Researchers have developed a machine that keeps the donated kidney at normal body temperature rather than keeping it cold, and supplies it with a blood-like fluid, similarly to how it would work in the body. This method is called Normothermic Machine Perfusion.

 

Testing the new method

Researchers from Oxford tested their preservation machine on 36 kidneys before being transplanted into patients who had agreed to take part in this study, then followed the recipients for 12 months after their transplants.

The machine works by pumping blood through the kidney at body temperature (around 37°C). It supplies oxygen and removes waste products, allowing the kidney to continue almost as normal while it is outside the body. The researchers could keep kidneys on this machine from 2 to 24 hours.

They compared the results with 72 similar patients from previous years who has received kidney transplants where the kidney had been preserved the traditional cold way. The researchers matched these comparison patients to make sure they had similar characteristics, including type of kidney donor and quality of the donor kidney.

 

What did they find?

1. The new method is safe to use

The study showed that the warm preservation method is safe to use, and all 36 patients who received kidneys preserved in this way survived beyond 30 days after their transplant. This matched the success rate of patients who received kidneys preserved in the traditional cold way. 

2. It results in similar kidney function

The kidneys that used the new method of preservation worked just as well after transplant as those using the traditional method. Kidney function was measured 12 months after transplant and was similar between patients who received warm-preserved kidneys and those who received cold-preserved kidneys. 

3. Kidneys can be preserved for longer

The researchers were able to keep one kidney preserved on the machine for 23.4 hours, which is the longest time any research group has kept a kidney preserved before being successfully transplanted. This shows that kidneys can survive outside the body for longer than previously thought when using this method. 

 

Benefits of the new method

The warm preservation method offers lots of potential benefits:

• Better scheduling: Transplant operations can be planned for daytime hours when full surgical teams are available, rather than emergency night time surgery.
• Kidney testing: The machine allows doctors to test how well a kidney is working before it is transplanted. It can measure urine production and blood markers to better predict whether or not a kidney will work well.
• Potential treatments: In the future, doctors may be able to use the machine to treat kidneys and improve their condition before being transplanted, rather than just preserving them.
• Increase suitable kidneys: This method might allow doctors to safely use kidneys that would otherwise be considered too risky for transplant, helping to increase the number of suitable kidneys available for those who need them.

 

Predicting kidney success

The researchers found that certain substances in the fluid around the kidney while its being preserved could predict how well it would work after being transplanted. The most important marker for predicting success was called GST-Pi (glutathione serum transferase), as researchers linked changes in levels of this marker during preservation to kidney function up to one year after transplant. This can give doctors a new way to assess the quality of a donated kidney before it is transplanted to someone with kidney failure. 

 

What does this mean for patients?

This research shows that this new machine offers a safe alternative to the traditional method of preserving donated kidneys before they are transplanted. While it did not lead to better kidney function compared to the traditional method, it still opens up new possibilities for improving the process of kidney transplantation.

The ability to keep kidneys healthy outside the body for up to 24 hours gives transplant teams more flexibility when scheduling operations and can help with assessing kidney quality. This could lead to more successful transplants and better outcomes for people with kidney failure.

The new technique can also be used for future research into treating kidneys before transplant to improve their function.

 

What next?

The researchers involved in this study suggest that future studies should test putting the donated kidney onto the machine sooner after donation, as the kidneys involved in this study spent some time in cold storage before reaching the machine. They also want to explore using the machine to deliver specific treatments to kidneys before they are transplanted.

This study was intended to test the safety of this machine; the next step would be to test it on a larger scale to see if it can improve the outcome of patients compared to current methods.

The researchers believe this technology could help more kidneys to become suitable for transplant that otherwise would not be used, potentially helping more patients to receive transplants who need them.

Read the full article

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Funding

This study was funded by the National Institute for Health Research and involved collaboration with OrganOx Ltd, who developed the preservation machine.

 

The original article

This is a summary of: Dumbill, R., Knight, S., Hunter, J. et al. Prolonged normothermic perfusion of the kidney prior to transplantation: a historically controlled, phase 1 cohort study. Nat Commun 16, 4584 (2025). Available at: https://doi.org/10.1038/s41467-025-59829-5 

This summary has been approved by a member of the research team.