People with long COVID may face an increased risk of abnormal blood clotting, according to the first study to look at the link between abnormal blood clotting tests and reduced exercise capacity.
Researchers from University College London Hospital found those experiencing difficulties with basic exercise more than 12 weeks after their COVID-19 infection were four times more likely to have blood markers indicative of a “pro-thrombotic state”, meaning they were at heightened risk of blood clotting.
The study, published in Blood Advances, provides important new insight into the potential mechanisms behind the longer-term effects of COVID-19 infection.
The research team, led by Prof Marie Scully, assessed people in an outpatient post-COVID clinic between July 2020 and May 2021.
Anyone who had experienced symptoms three months after the onset of their original COVID-19 infection, and if those symptoms persisted for at least two additional months, were classed as having long-COVID.
Researchers analysed the ratio of Von Willebrand factor (VWF) to ADAMTS13. If this ratio was raised – with significantly more VWF than ADAMTS13 in the bloodstream – patients were characterised as being in a pro-thrombotic state.
Participants completed exercise tests, performing timed activities such as walking on a flat surface and repeatedly going from sitting to standing position from a chair while wearing oxygen monitors.
Their oxygen levels were measured, and their blood tested before and after exercise to measure lactate levels. Patients who had a significant decrease in oxygen levels while exercising and/or a rise in lactate afterward were deemed to have an impaired exercise capacity.
The researchers found that these patients with impaired exercise capacity were four times more likely to have a raised VWF:ADAMTS13 ratio, and so more likely to be in a pro-thrombotic state.
Absolute levels of Factor VIII and VWF in the blood were also significantly raised in people with impaired exercise capacity.
Study lead author Nithya Prasannan said they now aim to assess patient bloodwork using different research platforms over the course of their long-COVID illness to assess how their risk of thrombosis might change with the progression of their symptoms.
This additional monitoring could not only help confirm possible mechanisms underlying long-COVID, but also offer insight into the effects of potential treatment options for the condition, she added.
“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,” said Dr Prasannan.
“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.”
Source: Prasannan N, Heightman M, Hillman T, Wall E, Bell R, Kessler A, Neave L, Doyle AJ, Devaraj A, Singh D, Dehbi HM, Scully M. (2022) “Impaired exercise capacity in post-COVID syndrome: the role of VWF-ADAMTS13 axis.” Blood Advances, doi:10.1182/bloodadvances.2021006944
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