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 reviewer(s) at the time of publication.

Why do kidneys need to be tested before transplant?

There are currently not enough healthy donated kidneys available for all the people who need to have a kidney transplant. Sometimes, doctors will use kidneys for transplant that are not perfect but will still work, and these need to be checked carefully to make sure they will function properly after being transplanted. 

Kidneys can be preserved while they are outside the body after being donated by using a technique called normothermic machine perfusion. This involves keeping the kidney at normal body temperature and allows time for doctors to test its quality, however these tests are currently not very good at predicting whether or not the transplant will be successful. 

If a kidney is damaged, blood flow through the tiny blood vessels inside can become poor, even when the main blood flow through the kidney seems normal. Researchers wanted to test if a special ultrasound technique could measure the blood flow in these small blood vessels to help doctors to better understand kidney quality before transplantation.

 

Using an ultrasound to test kidney quality

Researchers used a technique called contrast-enhanced ultrasound, which means injecting tiny bubbles into the blood that show up clearly on ultrasound scans. These bubbles are safe and do not harm the kidney. They are small enough to flow through even the tiniest blood vessels and give a clear picture of blood flow through the kidney. 

They tested this method on 8 kidneys from pigs and 5 kidneys from humans. The pig kidneys came from pigs that had died, and the human kidneys were ones that had been donated for transplant but were decided to be unsuitable for various reasons. 

They connected each kidney to a machine that pumps blood through it at body temperature, and during this process they performed ultrasound scans with the contrast bubbles to measure how well blood flowed through the kidney. 

The researchers also did other tests on the kidneys to check for damage, including looking at tissue samples to check for death of cells and measuring levels of a protein called NGAL, which increases when kidneys are damaged.

 

What did they find?

1. Better small blood vessel flow means healthier kidneys

The study showed that kidneys with better blood flow through the small blood vessels had less damage than ones with worse blood flow. In both the pig and human kidneys, the ones with better small blood vessel flow also had lower levels of the protein NGAL and had fewer dead cells in their tissue.

2. The ultrasound method can predict kidney damage

When the researchers did ultrasound scans early in the machine perfusion process, they could predict how much kidney damage there would be later. In human kidneys they could use ultrasound results that were taken after 2 hours to predict what the kidney would be like after 24 hours. 

3. General blood flow can be misleading

Researchers found that measuring the total amount of blood flow throughout the whole kidney was not a good way to judge kidney health. Sometimes, kidneys with a good level of total blood flow had worse levels of small blood vessel flow. This could be because the blood was taking shortcuts through the kidney rather than reaching all the parts that need it.

4. Creating tools for other researchers

The research team created a free computer program and website that other researchers can use to look at this type of ultrasound data and to use this method in their own studies.

 

What does this mean for people with kidney disease? 

This research could lead to better ways of checking if donated kidneys are good enough to be used for a transplant. Currently, some kidneys may be turned down because doctors cannot tell whether or not they will work, while some poor-quality kidneys may be used when they shouldn't be. 

The ultrasound method used in this study provides a number of benefits: it can be done quickly, it gives results straight away, and it does not harm the kidney.

It this method continues to work well when studied on a larger scale, it could help more people to receive successful kidney transplants. It could allow doctors to use more donated kidneys that would otherwise be discarded and help to ensure that kidneys being transplanted have the best chance of working well. 

 

What next?

This study was done using kidneys that did not end up being transplanted into people. The next step is to test this method in real transplant situations to see if it can predict which transplants will be the most successful. 

Researchers need to study more kidneys and check in with patients after their transplant to see how well their kidneys work. They also want to test whether this ultrasound method works with the different types of equipment that is used in different hospitals. 

The team also want to find out if this technique could be used to check the quality of other organs in the same way, such as livers. 

 

Why is this research important?

Every year, thousands of people die while waiting for kidney transplants because there are not enough donated kidneys available. At the same time, some donated kidneys are not used because doctors are not confident they are good enough quality. 

This research could solve two problems: it could help to ensure that more donated kidneys are used and it could help to ensure that the kidneys used are more likely to work well. 

As the technique is relatively inexpensive and does not require complex equipment, it could potentially be used in many different hospitals around the world. 

For people waiting for kidney transplants, this research represents a step towards more effective use of donated organs and potentially shorter waiting times for a transplant. For people who receive transplants, it could mean a better chance that their new kidney will work well for many years. 

Read the full article

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Funding

This study was funded by a Medical Research Council Clinical Research Training Fellowship which was partly funded by Kidney Research UK. This research was also funded in part by the Wellcome Trust. BG and CC, as well as some consumables supporting this research, were funded by a UKRI/MRC project grant. The human research in this study is partly funded by the National Institute for Health and Care Research (NIHR) Blood and Transplant Research Unit in Organ Donation and Transplantation, a partnership between NHS Blood and Transplant, University of Cambridge and Newcastle University.

 

The original article

This is a summary of: Tingle SJ, Connelly C, Glover EK, Stenberg B, McNeill A, Kourounis G, Gibson BG, Mahendran B, Bates L, Cooper MN, Pook RR, Lee S, Brown ML, Figueiredo R, Marchbank KJ, Ali S, Sheerin NS, Wilson CH, Thompson ER. Contrast-Enhanced Ultrasound to Assess Kidney Quality During Ex Situ Normothermic Machine Perfusion. Transpl Int. 2025 Apr 2;38:14268. doi: 10.3389/ti.2025.14268. PMID: 40242325; PMCID: PMC11999844. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC11999844/

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