- Researchers do not yet fully understand the mechanisms underlying the symptoms of a long COVID.
- A new study shows that 28% of people with long COVID have higher levels of markers linked to blood clot formation.
- Abnormal levels of these markers were associated with impaired exercise capacity but not other long-term COVID symptoms.
- These findings could inform future research on treatments to reduce such abnormalities related to blood clotting in people with long COVID.
A study recently published in the journal blood advances found elevated blood clotting markers in more than one in two (55%) people with long COVID who also had abnormal stress test results.
People with elevated blood clotting markers were four times more likely to have sustained deficits in exercise capacity.
These results suggest that people with long COVID should be screened for impaired exercise capacity and markers related to blood clotting. The author of the study, Dr. Nithya Prasannan, a researcher at University College London Hospital says:
“I hope people will view this research as a step forward in understanding what is causing long COVID, which will hopefully help us guide future treatment options.”
More than 500 million people worldwide have been diagnosed with COVID-19 so far, according to the World Health Organization. Although estimates vary widely, a recent meta-analysis suggests that nearly a third of all people with COVID-19 may have persistent symptoms 3 months after symptoms begin.
These COVID-19 symptoms, which persist for at least three months after SARS-CoV-2 infection, have been collectively described as “
Despite the growing number of people with long-term COVID, the mechanisms underlying these persistent symptoms of COVID-19 are not well understood.
Recent studies have shown that individuals with long COVID are more likely to develop
Acute COVID-19 is associated with an increased risk of blood clots. Consequently, people with acute COVID-19 are more likely to have elevated levels of proteins that promote blood clotting.
One such protein is von Willebrand factor (VWF), which helps form a clot to seal off damaged blood vessels at the site of injury. An enzyme called ADAMTS13 then breaks down the VWF protein into smaller fragments to reduce its activity and prevent clots from forming in blood vessels.
An elevated ratio of VWF to ADAMTS13 is associated with an increased risk of blood clots in acute COVID-19. Such a condition, which involves an increased risk of blood clots, is referred to as a prothrombotic condition.
In the present study, the authors examined whether such a prothrombotic condition was associated with the severity of long-term COVID symptoms, including exercise capacity.
The present study consisted of 330 people who had persistent symptoms 3 months or more after SARS-CoV-2 infection and attended a long outpatient COVID clinic. The majority (83%) have never been to the hospital.
At the time of the visit, the researchers conducted two tests to assess the participants’ endurance and physical capacity. These stress tests involved walking at a normal pace for 6 minutes and alternating from a sitting to a standing position repeatedly for 1 minute.
Researchers used an oxygen meter to measure blood oxygen levels during the test. They also measured changes in blood lactate levels, which the body produces when the oxygen supply is insufficient to sustain muscle activity.
To assess the risk of blood clotting, the researchers used blood samples to categorize participants into two groups based on whether their VWF/ADAMTS13 ratio was normal (less than 1.5) or abnormal (greater than or equal to 1.5).
The researchers found that about 28% of study participants had abnormal levels of VWF/ADAMTS13. The VWF/ADAMTS13 ratio did not correlate with the severity of long-term COVID symptoms, including headache, fatigue, and cognitive deficits.
However, abnormal VWF/ADAMTS13 levels were associated with impaired exercise capacity, as measured by blood oxygen and lactate levels. Almost 20% of the participants showed limited physical capacity and 55% of the people in this group had elevated levels of VWF/ADAMTS13.
Elevated levels of VWF/ADAMTS13 were four times more likely in exercise-impaired individuals than in those with normal ability in the exercise tests. In addition, levels of VWF and the blood clotting protein factor VIII were also higher in people with reduced physical capacity.
dr Artur Fedorowski, Professor at Karolinska University Hospital, Stockholm, Sweden spoke to us MNT about the study. he w
“The higher VWF/ADAMTS13 ratio may indicate that some long-COVID patients have a predisposition to microclot formation, potentially affecting normal blood flow through various critical areas such as the lungs or cerebral circulation.” Thus, in the normal state, the patient may feel normal and compensated, while physical or mental exertion may reveal a lack of compensatory reserve and produce characteristic symptoms.”
“This hypothesis is mechanistically very attractive, but we should keep in mind that the majority of long COVID patients had a normal VWF/ADAMTS13 ratio. Either the abnormality detected is just one of many symptom-producing mechanisms of a long COVID, or there may not be a causal relationship.”
“Instead, the really long COVID mechanism can cause symptoms and an elevated prothrombotic ratio in some susceptible patients,” added Dr. Added Fedorovsky.
dr Prasannan spoke about future research directions MNT“Assessment of the VWF/ADAMTS13 ratio has become part of the routine assessments performed in long-COVID patients.”
“As part of ongoing research at the Haemostasis Research Unit, a shear flow-based assay (a platform that mimics blood flow through blood vessels) is being used to study microclot formation in patients with long-term COVID.”