Approximately 100 million people worldwide currently suffer from long COVID, a condition experienced as lingering and/or new symptoms following a COVID-19 infection and lasting for more than four weeks (according to the CDC’s definition). Scientists have known since early 2020 that COVID-19 is more than a lung disease; the SARS-CoV-2 virus seriously impacts the body’s vascular system, affecting both blood flow and blood clotting. 

One of these scientists, Dr. Resia Pretorius, a distinguished researcher and head of the physiological sciences department at Stellenbosch University in South Africa, led a study that revealed significant microscopic blood clot or “microclot” formation in both acute COVID-19 and long COVID patients. 

Why Are Microclots a Concern?

Persistent microclots and hyperactivated platelets (platelets made more prone to forming clots by inflammatory proteins) increase the risk of tissue cells not getting enough oxygen to maintain bodily functions. This lack of oxygen is called cellular hypoxia. Widespread hypoxia may be a core contributor to the numerous debilitating symptoms of long COVID sufferers, including:

• Breathlessness
• Fatigue
• Muscle weakness
• Low oxygen levels
• Sleep disturbances
• Anxiety and depression
• Elevated risk of heart attacks and stroke

In a healthy person, the body breaks down blood clots through fibrinolysis, a process in which enzymes cut through the fibrous mesh of the clot, allowing blood to flow. In people with long COVID, however, researchers have found microclots that are resistant to the body’s natural fibrinolytic processes. 

Pretorius’ research team also found high levels of inflammatory molecules trapped inside the microclots, including clot-promoting proteins, and the molecule Alpha-2 antiplasmin, that prevents microclot breakdown.

Treating Clots in COVID-19 Long-Haulers

Unfortunately, the inflammatory proteins are often not detected during routine blood tests, so “many desperately ill patients are being told that their pathology test results are within normal/healthy ranges, and that their symptoms may be psychological,” writes Pretorius. Traditional lab tests fail to detect the inflammatory molecules, she says, because they’re hidden inside the fibrinolytic-resistant microclots that are only visible under a fluorescence or bright-field microscope. When the soluble plasma content is measured, the inflammatory proteins don’t stand out.

Fortunately, preliminary results suggest that antiplatelet and anticoagulation treatments have shown encouraging results in long COVID patients, provided there is close professional monitoring of patients due to the danger of bleeding. Pretorius adds that a procedure called HELP (heparin-induced, extracorporeal, lipoprotein/fibrinogen precipitation), a process in which microclots and inflammatory molecules are filtered out dialysis-style, may also be beneficial. 

Now that scientists and medical professionals know what to look for, Pretorius concludes, the U.S. needs to invest in more research and clinical trials to better understand and, ultimately, address, the relationship between abnormal blood clotting, hypoxia, and vascular dysfunction in long COVID patients. 

*Pretorius, R. (2022, Jan. 5). Could Microclots Help Explain the Mystery of Long COVID? The Guardian.   https://www.theguardian.com/commentisfree/2022/jan/05/long-covid-research-microclots?