Months after the acute phase of Covid-19 has passed, something in the blood of long Covid patients continues to stir — a persistent elevation in clotting markers that Irish researchers at the Royal College of Surgeons now believe may lie at the very heart of the condition's enduring grip. Published in the Journal of Thrombosis and Haemostasis, the study of fifty long Covid patients found that this coagulation disturbance correlates directly with fatigue and diminished physical capacity, and that it persists even after the body's inflammatory signals have quieted. The finding matters not only a
Irish study links elevated blood clotting to long Covid fatigue and reduced fitness
Millions of people worldwide are affected by long Covid syndrome with persistent symptoms including fatigue and reduced physical fitness.
Clotting may be the root cause, not just a symptom
Mark
So they found that long Covid patients have thicker blood, essentially? Is that the takeaway?
Mimi
Not quite thicker blood—elevated clotting markers. It's a measurable sign that the coagulation system is more active than it should be. The blood itself isn't necessarily thicker, but the chemistry that controls clotting is out of balance.
Luke
And they measured this in fifty people. That's a real sample, but it's not huge. Are these fifty representative of all long Covid patients, or is there selection bias we should know about?
Mimi
The source doesn't specify how they recruited the fifty, so that's a fair question. What we do know is the elevation showed up across the board—hospitalized and non-hospitalized patients both had it.
Mark
Why does this matter if inflammation markers are normal? Doesn't that mean the acute phase is over?
Mimi
That's exactly what makes it interesting. It suggests the clotting problem isn't just a leftover from inflammation. It might be its own thing—a separate mechanism keeping people fatigued and deconditioned.
Luke
But they haven't proven causation yet, right? They found correlation—higher clotting correlates with worse fatigue. That's not the same as proving clotting causes the fatigue.
Mimi
Correct. They've identified an association. The next step would be intervention studies—treating the clotting and seeing if symptoms improve.
Mark
How many people are we talking about with long Covid globally?
Mimi
Millions, according to the researchers. The source doesn't give a precise number, but it's clearly a large population.
Luke
And this study was funded by reputable sources—Wellcome Trust, the Health Research Board. That's credible backing, which matters for a finding like this.
Il Polso
- Millions of people worldwide remain trapped in a post-infection limbo, unable to regain their former energy or fitness despite technically clearing the virus.
- A study of fifty long Covid patients reveals their blood clotting systems are still running hot — significantly elevated above healthy controls — even in those who never needed a hospital bed.
- Crucially, inflammation markers have normalized in these patients, meaning clotting is not simply trailing behind other illness signals but may be operating as an independent, primary force.
- The severity of clotting elevation maps directly onto how fatigued and physically deconditioned patients feel, giving researchers a measurable biological thread to pull.
- With infections continuing among unvaccinated populations, scientists warn the burden of long Covid will only deepen, making the urgency of this research difficult to overstate.
- If clotting is confirmed as a root driver of long Covid, targeted anticoagulation therapies could move from possibility to priority — shifting treatment from symptom management toward genuine recovery.
Months after the acute phase of Covid-19 has passed, something in the blood of long Covid patients continues to stir — a persistent elevation in clotting markers that Irish researchers at the Royal College of Surgeons now believe may lie at the very heart of the condition's enduring grip. Published in the Journal of Thrombosis and Haemostasis, the study of fifty long Covid patients found that this coagulation disturbance correlates directly with fatigue and diminished physical capacity, and that it persists even after the body's inflammatory signals have quieted. The finding matters not only as a biological clue, but as a potential doorway toward treatments that address cause rather than consequence — a distinction that could alter the lives of millions still waiting to recover.
Researchers at Ireland's Royal College of Surgeons have identified something unusual persisting in the blood of long Covid patients long after their initial infection has cleared: elevated clotting markers suggesting the body's coagulation system remains in a state of heightened activity. The findings, published in the Journal of Thrombosis and Haemostasis, may offer the clearest biological explanation yet for why so many people continue to experience fatigue and reduced physical capacity months after recovery.
The study compared blood chemistry in fifty long Covid patients against healthy controls and found clotting markers significantly elevated across the group. Notably, the elevation appeared regardless of initial illness severity — hospitalized patients showed the highest levels, but those who recovered at home still carried persistently abnormal readings.
Lead researcher Dr. Helen Fogarty highlighted a detail that sharpens the finding considerably: inflammation markers — the body's standard alarm signals — had returned to normal in these patients, while clotting remained disturbed. This suggests the coagulation abnormality is not a downstream effect of lingering inflammation, but potentially a primary driver of long Covid's stubborn symptoms. The degree of clotting elevation tracked directly with how fatigued and physically diminished patients reported feeling.
Professor James O'Donnell, director of the Irish Centre for Vascular Biology, stressed that identifying root causes is the essential precondition for developing effective treatments, and that the problem will grow as infections continue. For the millions living with long Covid, the research represents something more than a scientific milestone — it is the beginning of a map toward reclaiming what the illness took.
Researchers at Ireland's Royal College of Surgeons have identified a persistent abnormality in the blood of long Covid patients that may explain why millions of people continue to suffer fatigue and reduced physical capacity months after their initial infection has cleared. The finding, published in the Journal of Thrombosis and Haemostasis, centers on elevated clotting markers—measurable signs that the blood's coagulation system remains in a heightened state even as other signs of acute illness fade.
The study examined fifty patients experiencing long Covid symptoms and compared their blood chemistry to healthy controls. What emerged was striking: clotting markers were significantly elevated across the long Covid group. Importantly, this elevation appeared regardless of how severely the initial infection had struck. Patients who had required hospitalization showed the highest clotting markers, but those who managed their acute illness at home still carried persistently elevated levels. The pattern held steady.
Dr. Helen Fogarty, the study's lead researcher and a PhD student at the Irish Centre for Vascular Biology, noted that the clotting abnormality persisted even as inflammation markers—the body's alarm signals—had returned to normal ranges. This distinction matters. It suggests the clotting system may not be a secondary consequence of lingering inflammation but rather a primary driver of long Covid's stubborn symptoms. The researchers found a direct relationship between the degree of clotting elevation and the severity of fatigue and physical deconditioning patients reported.
Long Covid remains poorly understood. Symptoms can persist for weeks or months after the acute infection resolves, and the condition is estimated to affect millions of people worldwide. Previous research from the same group had documented dangerous clotting in patients with severe acute Covid-19, but the mechanisms behind long Covid's persistence have remained largely opaque. This study offers a concrete biological marker that might explain why so many people find themselves unable to return to their previous level of activity, even after they have technically recovered from the virus.
Professor James O'Donnell, director of the Irish Centre for Vascular Biology and a consultant haematologist at St James's Hospital in Dublin, emphasized that identifying the root cause of a disease is essential before effective treatments can be developed. He noted that the problem will only grow as infections continue among unvaccinated populations, making the research urgent. The work was supported by the Wellcome Trust and the Health Research Board, including funding from the Irish Covid-19 Vasculopathy Study.
The implications are substantial. If clotting is indeed central to long Covid's pathology, it opens a path toward targeted interventions—treatments designed specifically to address the coagulation abnormality rather than merely managing symptoms. For the millions already living with long Covid, understanding what is happening inside their blood vessels represents a first step toward reclaiming their former capacity.
Citazioni salienti
Because clotting markers were elevated while inflammation markers had returned to normal, our results suggest that the clotting system may be involved in the root cause of long Covid syndrome.— Dr. Helen Fogarty, lead author
Understanding the root cause of a disease is the first step toward developing effective treatments. Millions of people are already dealing with the symptoms of long Covid syndrome.— Professor James O'Donnell, director of the Irish Centre for Vascular Biology
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