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Scientists probe link between COVID symptoms, blood clots

Studies has suggested that fewer than a third of patients who have ongoing COVID symptoms after being hospitalised with the disease feel fully recovered 12 months later.

Now UK researchers are investigating a possible link between blood clots and these ongoing symptoms, with a series of trials to explore whether blood thinners may help those who have had the disease, reports The Guardian.

Professor Ami Banerjee of University College London, who is leading a study called Stimulate-ICP, said it was known COVID infection increases the risk of blood clots, and that people who have had the disease have a greater risk of related conditions including stroke, heart attacks and deep vein thrombosis.

In addition, Banerjee said research from scientists in South Africa had suggested that people with long COVID have micro-clots in their blood, while studies in the UK suggested almost a third of long-COVID patients have clotting abnormalities.

But he said it was not clear if the findings were generalisable. Although there had been calls on social media for anti-coagulants to be made available on the basis of such findings, further research was needed, particularly as blood thinners can lead to an increased risk of bleeds.

Professor Betty Raman of the University of Oxford concurred with Banerjee, warning that studies into micro-clots and long COVID had not yet been carried out on a large scale, that micro-clots were difficult to screen for, and it was not yet clear whether clotting abnormalities are indeed a cause of ongoing COVID symptoms.

"More dedicated studies are needed, looking at the efficacy of anti-coagulants (for long COVID), just as we did with (treatments for) the acute unwell patients,” Raman said.

The Stimulate-ICP trial, due to start recruiting within days, will split 4,500 people with long COVID into four groups in which participants are allocated usual care, antihistamines, an anti-inflammatory or an anti-clotting drug for three months. “That will allow us to say whether that improves the fatigue and other outcomes of people with long COVID,” said Banerjee.

While the trial focuses on people who had COVID in the community, another study, called Heal-COVID, involves people who were hospitalised with the disease, aiming to identify treatments that may help to prevent or reduce ongoing symptoms.

“Heal-COVID is not a study treating people with long COVID: we are aiming to prevent things getting to that point,” said Professor Charlotte Summers of the University of Cambridge, chief investigator.

The team has recruited 1,118 participants, with one arm of the trial involving participants receiving blood thinners. “The trial included anti-coagulants as there was thought to be an increased number of large blood clots occurring in the post-hospital phase of the illness rather than micro-clots,” Summers said.

The post-hospitalisation COVID-19 study – or Phos-COVID – which has offered key insights into long COVID, is also probing the issue of clotting.

Chris Brightling, a professor of respiratory medicine at the University of Leicester and chief investigator on the study, said one area the team was looking at was whether people with ongoing symptoms after hospitalisation have chronic thromboembolic pulmonary hypertension. Should this be found, he said, it would be strong evidence that micro-clots are a substantial problem.

“Whereas if we don’t see that, that doesn’t exclude the possibility that, obviously – certain individuals get clots – but it would make it less likely that it’s intrinsically a major problem,” he said.

Banerjee said that while it was understandable some patients with ongoing symptoms of COVID may be frustrated that certain therapies were not yet available, rigorous studies were essential. “We need to make sure that we don’t (lower) the bar for safety,” he said.


Stimulate-ICP (open access)


The Guardian – Possible link between blood clots and Covid symptoms investigated


See more from MedicalBrief archives:


Microclot formation may have ‘long COVID’ implications – Stellenbosch


Long COVID: More than a quarter of patients still symptomatic after six months — Swiss study


Long COVID-19 may have affected 2m in England – REACT-2




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