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Blood marker identifies Covid patients with no symptoms

Cambridge researchers have discovered a biomarker in blood that could help identify those who caught Covid-19 months ago – even if they had no symptoms.

Now the team, at Cambridge University Hospital NHS Foundation Trust the University of Cambridge, has received £370,000 from the National Institute for Health Research (NIHR) to develop a Covid-19 diagnostic test that will complement existing antibody tests, and a test that could diagnose and monitor long Covid.

The research builds on a pilot project supported by Addenbrooke’s Charitable Trust and patients from the hospital’s Long Covid Clinic established in May 2020.

A total of 85 patients were recruited to the Cambridge NIHR Covid BioResource, which collected blood samples at first diagnoses and over several months. Now it is hoped to expand the cohort to 500 patients.

The team identified a biomarker – a biological fingerprint – in the blood of patients who previously had Covid-19. Known as a cytokine, the molecule is produced by T cells in response to infection and persists in the blood for a long time. The team plans to publish their results shortly.

Mark Wills - head and shoulders
Dr Mark Wills

Team co-lead, Dr Mark Wills from the Department of Medicine at the University of Cambridge, said: “We need a reliable and objective way of saying whether someone has had Covid-19. Antibodies are one sign we look for, but not everyone makes a very strong response and this can wane over time and become undetectable.

We’ve identified a cytokine that is likely to be detectable for several months – and potentially years – following infection. We believe this will help us develop a much more reliable diagnostic for those individuals who did not get a diagnosis at the time of infection.

Dr Mark Wills

By following patients for up to 18 months post-infection, the team hopes to address whether immunity wanes over time and whether people who were vaccinated will need boosters to keep them protected.

The team also identified a biomarker found in patients with long Covid. Their work suggests these patients produce a second type of cytokine, which persists in patients with long Covid compared to those that recover quickly and might be one of the drivers behind the many symptoms that patients experience.

Dr Nyarie Sithole
Dr Nyarie Sithole

Fellow co-lead, Dr Nyarie Sithole, a consultant in infectious diseases and acute medicine at Addenbrooke’s Hospital, said:

Because we currently have no reliable way of diagnosing long Covid, the uncertainty can cause added stress to people who are experiencing potential symptoms. If we can say to them ‘yes, you have a biomarker and so you have long Covid’, we believe this will help allay some of their fears and anxieties.

Dr Nyarie Sithole

The team is using the tests for research purposes, but by increasing the size of their study cohort and carrying out further work, they hope to adapt and optimise it for use by clinical diagnostic labs.