Analysis of over 13 million health records finds increased risk to kidneys in only severe COVID-19 infections
A new study of over 13 million people in England has found no evidence to suggest mild COVID-19 infection may cause long-term kidney damage. However, patients hospitalised with severe COVID-19 infections are at a high risk of long-term kidney damage, the analysis suggests.
Over the course of the COVID-19 pandemic, severe infections requiring hospitalisation were often accompanied by a decline in kidney function. While research studies continue to support this association, until now it has remained unclear whether milder COVID-19 infections, which do not require treatment in hospital, may also affect kidney function long-term.
The new study, led by researchers at the London School of Hygiene & Tropical Medicine (LSHTM) as part of the OpenSAFELY collaboration with the University of Oxford, analysed electronic health data from over 13 million GP and hospital records in England between 1 February 2020 and 31 December 2022.
The OpenSAFELY platform acts as a gateway between electronic patient records and important medical research. Developed over the COVID-19 pandemic, the platform allows information from GP records to be anonymised, grouped with other sources of data such as hospital records, and used in scientific studies, without researchers having direct access to the records or identifiable information.
Of the data analysed in the study, over 3.5 million people were recorded as having had a COVID-19 infection and 10 million people did not have a record of infection. Records from people who were already on dialysis, a treatment used to filter blood when a patient's kidneys are unable to do so, or living with a kidney transplant, were excluded from the sample.
The findings are published in The Lancet Regional Health Europe.
Across the study period, people who needed hospitalisation for COVID-19 had over seven times greater risk of kidney failure than people without COVID-19. These risks were highest amongst those who required intensive care and in those recorded as having acute kidney injury during their illness. Amongst people with COVID-19 which was not severe enough to require hospitalisation, there was no increased risk of kidney failure.
Dr Viyaasan Mahalingasivam, a research fellow at LSHTM and a specialist kidney doctor at Barts Health NHS Trust, and lead author of the study, said: "Our study is the largest of its kind to look at the long-term effects of COVID-19 infections on our kidneys. During the heights of the pandemic, we were overwhelmed by the volume of patients who were sick with COVID-19 who needed dialysis for severe kidney injury. Because of this, there were concerns that milder COVID-19 illness might lead to more gradual kidney damage over the longer term.
"It's reassuring that we did not find evidence to suggest that mild COVID-19 infection causes long-term damage to kidney function. But we can't ignore that those who experience severe illness with COVID-19 and end up in hospital, do have a high risk of kidney failure or worsening kidney function.
"Our work builds on previous studies which have suggested that kidney complications may be a bigger problem after COVID-19 than other types of infection. However, we're not able to say whether the main mechanism behind this is the COVID-19 virus attacking the kidney directly or if it is a consequence of the body's inflammatory response to severe infection."
The study also found that the increased risk of kidney damage for patients hospitalised with COVID-19 infections differed across ethnicities and was highest for black ethnic groups.
Dr Laurie Tomlinson, Professor of Clinical Epidemiology at LSHTM and a senior author of the study, said: "Our results show that having a mild COVID-19 infection does not increase your risk of getting long-term kidney damage, and that is particularly reassuring for patients who are already living with kidney disease. However, there were still a substantial number of people who were admitted to hospital for COVID-19 infections, who then went on to develop kidney failure and it's important that we try to establish how we can minimise this in future.
"Our findings all add to growing calls for more studies into health inequalities and what could be driving them, such as delayed access to treatment, differing susceptibility to infections and broader structural and social determinants of health."
The authors say that healthcare providers should prioritise interventions which minimise the chances of at-risk groups needing hospitalisation. This includes ensuring vaccinations can be accessed by patients who are most vulnerable to severe illness. They say that patients discharged from hospital after being treated for COVID-19 infection should also be carefully monitored.
The research was funded by the National Institute for Health and Care Research.
Publication
Mahalingasivam V, Zheng B, Wing K et al. Long-term kidney outcomes after COVID-19: a matched cohort study using the OpenSAFELY platform. Lancet Regional Health Europe. DOI: https://doi.org/10.1016/j.lanepe.2025.101338
