Blood-thinning drugs could help save lives of Covid-19 patients, say medical researchers, as they discover a link between the virus and blood clots in the lungs.

Specialists at Royal Brompton Hospital’s severe respiratory failure service have established a clear link between Covid-19 and blood clotting, by using hi-tech CT scans to take images of lung function in critically-ill patients.

All of those tested suffered a lack of blood flow, suggesting clotting within the small vessels in the lung.

Royal Brompton said this could partly explain why some patients are dying of lung failure through lack of oxygen in the blood.

If these interventions in the blood are implemented appropriately, they will save lives

Doctors believe that careful use of the drugs, known as anticoagulants, can eventually save lives, but testing will need to be extremely careful as the drugs can also have serious consequences.

They said a blanket use of anticoagulants would not be appropriate and that any treatment would have to start very early to prevent clots forming.

Dr Brijesh Patel, senior intensivist and clinical senior lecturer at Royal Brompton and Imperial College London, said: “These are very unwell patients but I think the majority of patients will end up on significant therapeutic doses of blood-thinning agents as we learn more about this disease.

“If these interventions in the blood are implemented appropriately, they will save lives.”

Other European studies found signs of blood clotting in a third of coronavirus patients, but Dr Patel explained “we have to be cautious” with how we proceed with blood thinning agents.

All the time we are discovering new twists and this intravascular clotting is a really nasty twist that we haven't seen before with many other viruses

“You have to do it in the right way otherwise you can cause harm,” said Dr Patel.

“There are a variety of blood-thinning agents as well. Which (drug) you use depends on the patient so we have to have a more personalised medicine approach.”

Professor Peter Openshaw, a specialist in experimental medicine at Imperial College London and honorary physician at St Mary’s hospital, expressed optimism over the discovery.

“It does sort of explain the rather extraordinary clinical picture that is being observed with people becoming very hypoxic, very low on oxygen and not really being particularly breathless,” he said.

“That would fit with it having a blood vessel origin.”

Immunothrombosis experts at Hammersmith Hospital and Royal Brompton are also looking at the link between immune inflammation and blood clotting.

“It’s an unprecedented amount of collaboration and development of a really quite extraordinary story about a virus that we hitherto knew nothing,” said Prof Openshaw, a member of the Scientific Advisory Group for Emergencies (Sage) sub-group on clinical information.

“All the time we are discovering new twists and this intravascular clotting is a really nasty twist that we haven’t seen before with many other viruses.”

Dr Patel added: “We’ve seen over 150 patients that have come through the Royal Brompton and having had a look at many of them over the past couple of months we’ve learnt a lot about them.”