Research from the Royal College of Surgeons in Ireland (RCSI) has looked at why some Covid patients are experiencing blood clotting issues long after the infection. What impact might this have on people who are still suffering with long Covid and is it something that only effects those who had severe covid?

Dr Helen Fogarty from the School of Pharmacy and Biomolecular Sciences at RCSI talked to RTÉ Radio 1's Today with Claire Byrne about the links between long Covid and blood clotting. (This piece includes excerpts from the conversation which have been edited for length and clarity - you can hear the discussion in full above.)

RCSI research has found that one in four Long Covid patients are still showing unusual blood clotting activity up to a year later. "Our lab research team has now been studying clotting proteins and Covid since the very early days of the pandemic. What we know, is that Covid-19 infection is associated with a very high risk of developing a potentially fatal blood clot, such as maybe a clot in the leg, a lung, or even a stroke."

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"What we found during acute Covid-19, was that these clotting protein levels were massively increased and they were higher in patients with severe illness. For example those who needed an ICU admission and patients who unfortunately died of Covid, compared with those who had mild illness. Some of these clots can even develop after a patient has been discharged from hospital and while they're recovering from their initial illness." Unlike acute Covid-19, we know a lot less about long Covid, which is affecting millions of people around the world. says Fogarty.

The study examined patients attending the long Covid clinic in Saint James's Hospital in Dublin, three months after infection. Around two thirds of them had been hospitalised but a third had not. "We found that those clotting markers were still really high in patients with long Covid compared with controls. In real terms, that's about 20 to 25% of these patients had abnormally high levels of clotting proteins."

The study showed that levels of clotting proteins were highest in patients who had severe illness, Fogarty explains. "But they were still high even in patients who managed their acute disease at home. That was quite surprising to us, as we probably only expected to see this in the sickest of patients."

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Tests for the blood clotting proteins wouldn't be routinely examined in the patients attending long Covid clinics, says Fogarty. But patients who had symptoms of clotting, such as pain in their leg, leg swelling, shortness of breath or chest pain, would be considered for potentially having a blood clot, with further radiological and imaging investigations performed.

"Some patients do develop these blood clots after they've gone home from hospital or after their illness, so if anyone was to experience leg swelling or severe shortness of breath or chest pain they should definitely seek medical attention," says Fogarty.

Research done in South Africa first described the term "microclots" in the context of Covid, which are tiny blood clots that "are only possibly to see under a special type of microscope," Fogarty explains. "These microclots were not present in healthy individuals, but they were able to see microclots in the blood of long Covid patients." It's still considered a "controversial" idea because there aren't standard tests for detecting the microclots." We need to see these data being replicated in larger studies around the world, first, to prove that microclots really do exist in long Covid, and secondly, to see if they're causing long Covid symptoms."

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The RCSI research showed that patients with long Covid have ongoing inflammation in particular cells. "Our research lab are particularly interested in a certain type of blood cell called an endothelial cell. These cells are important because they line the blood vessels throughout our body. When they become damaged or when they're attacked, these endothelial cells become activated and they can actually release a number of blood clotting factors."

"One of them that we're particularly interested in is called von Willebrand factor, which is found to be very high in patients with acute Covid and also in long Covid. But we also found that markers of new blood vessel formation and blood vessel growth were abnormal in long Covid patients. That would suggest that the damage to blood vessels during acute Covid-19 is still present, maybe in particular in the small blood vessels of the lungs which are the primary target of the SARS-CoV-2 virus, and that this may take quite a long time to heal."

Fogerty stressed that they've seen that patients do "absolutely" recover from long Covid, despite symptoms persisting for anywhere between three months to over 12 months. "It's quite a difficult syndrome to treat because it's so broad. It's not just shortness of breath or fatigue, but there's other symptoms like brain fog, so really it requires a kind of multidisciplinary approach. But there is hope and patients to recover."