A doctor who spent a week in intensive care with coronavirus has been revealed as an antibody "super-donor" who could save the lives of other people.
Alessandro Giardini, 46, has the highest antibody level in his plasma measured so far in a trial - around 40 times that of the average patient.
The discovery was made as part of an NHS trial to analyse the blood of 435 COVID-19 patients.
Mr Giardini, a consultant in the cardiology department of Great Ormond Street children's hospital, spent seven days on a ventilator in intensive care after falling ill with COVID-19.
He described being ill with the virus as a "very hard experience" as he did not know if he would see his wife and two children again.
He said he felt he "had to give back" by donating his convalescent plasma to help other patients.
Mr Giardini added: "Even though it was scary to go back into a medical environment and have a needle again, I really felt that if there was any chance I could help someone else who was still ill with COVID-19, that I needed to do it.
NHS Blood and Transplant (NHSBT), which is collecting the plasma for the trial, is appealing to recovered COVID-19 patients, especially men aged over 35 or those have been admitted to hospital, to come forward.
Research found that men were twice as likely (34%) to have high enough antibody levels compared to women (17%).
And only 10% of people aged under 35 had high enough antibody levels compared to 31% of 35-to-45-year-olds and 40% of those aged over 45.
Meanwhile, 70% of people admitted to hospital with coronavirus had high enough antibody levels compared to 31% of donors who had a positive test for COVID-19 but did not require hospital treatment.
Professor David Roberts, NHSBT's associate medical director for blood donation, said: "People who are more seriously ill produce more antibodies, which can be transfused to potentially help others.
"The evidence so far is that men and older people are more seriously affected by coronavirus."
People who believe they are eligible to take part in the donation programme are urged to contact NHSBT on 0300 123 23 23 or by visiting www.nhsbt.nhs.uk.
They will also need to be able to travel to one of the 23 donor centres, located in London, Manchester, Cambridge, Luton, Nottingham, Sheffield, Leicester, Bradford, Leeds, Newcastle, Lancaster, Liverpool, Stoke, Birmingham, Bristol, Gloucester, Oxford, Southampton, Poole and Plymouth.