WASHINGTON — A common symptom for people with long COVID is fatigue, and a recent study reveals those that are too tired to exercise might also have a higher risk of developing blood clots. The risk is four times higher among patients who could not perform basic exercises in comparison to those who could still continue to work out. The findings could help pinpoint how long COVID causes widespread damage to people’s bodies.
The exact cause behind long COVID remains unclear, but past research estimates that almost half of all COVID patients continue to have lingering symptoms months after their infection.
“By definition, this syndrome occurs when one experiences COVID-related symptoms long after the onset of infection that we can’t attribute to any other cause or diagnosis,” says Nithya Prasannan, study author and researcher at the Department of Hematology at the University College London Hospital, in a media release. “This study offers us laboratory and clinical evidence to begin to understand why some people experience long COVID symptoms.”
The team tracked the recovery of people with long COVID who attended an outpatient clinic between July 2020 and May 2021. Researchers diagnosed patients with long COVID if they continued to show symptoms three months from their initial infection and if the symptoms persisted for at least two months.
Blood clotting linked to oxygen levels
Researchers collected blood samples and measured the ratio of two proteins linked to blood clotting. Specifically, they compared the amount of a protein called Von Willebrand factor (VWF) to ADAMTS13.
ADAMTS13 cuts up VWF to stop it from blocking blood vessels. A higher ratio would indicate there would be more VWF than ADAMTS13 in people’s blood, suggesting a person has a higher chance of having blood clots.
As part of the study, the participants had their oxygen levels measured while doing several physical activities, including walking on a flat surface or changing from a sitting to a standing position on a chair. They measured oxygen levels and blood tests before and after the exercises to measure the change in lactate levels — a way to look at people’s endurance levels during low-intensity exercises. Lactate levels increase during exercise when the body can no longer turn sugar into energy because oxygen levels are low. Lactate compensates for the depleted oxygen levels, which can create energy without oxygen.
Study authors considered participants who showed low oxygen levels from the exercises and high lactate levels to have impaired exercise capacity. The researchers observed people with an impaired exercise capacity were four times more likely to develop more blood clotting markers. Based on the results, the team hopes to continue studying patients with long COVID’s bloodwork and their risk of thrombosis.
“I hope that people will view this research as a step forward in understanding what causes long COVID, which will hopefully help us guide future treatment options,” Dr. Prasannan explains. “I encourage people experiencing long COVID to participate in clinical trials when available because the more data we have, the better we can understand this condition.”
The study is published in the journal Blood Advances.