Inflammation Overload Triggers 'Microclots' in COVID Long-Haulers

Months after COVID symptoms have subsided, some individuals continue to grapple with the lingering effects of the infection. What’s most frustrating is that it’s difficult to predict which COVID survivors will go on to become so-called long-haulers. This diverse group includes both the young and old, hospitalized patients, and those who recovered after only experiencing mild symptoms.

Some estimates state that about 10 percent of COVID patients become long-haulers, driving researchers to take a closer look at the biological mechanisms influencing this phenomenon.

A new study published in Cardiovascular Diabetology reports yet another worrying long-term consequence of COVID: the formation of microscopic blood clots.

The researchers, led by Resia Pretorius from Stellenbosch University (SU), analyzed blood samples collected from COVID survivors experiencing symptoms such as shortness of breath, sleep difficulties, fatigue, weakness, anxiety, and depression. Because of the nature of the symptoms, Pretorius and colleagues hypothesized that long-haulers may not be able to absorb oxygen as efficiently in the aftermath of the infection. Blood clots clogging the fine microcapillaries in the lungs may be to blame for this compromised respiration. 

Pretorius’ team used a suite of protein characterization and fluorescence microscopy tools to test their theory, revealing evidence that supported their initial suspicions.

“We found high levels of various inflammatory molecules trapped in micro clots present in the blood of individuals with Long COVID,” said Pretorius. “Some of the trapped molecules contain clotting proteins such as fibrinogen, as well as alpha(2)-antiplasmin.”

These results point to an imbalance in the body’s blood clotting mechanisms in long-haulers. Under normal conditions, there’s a constant molecular tug of war in the circulation—fibrinogen makes the blood clot to prevent blood loss after injury, and a process known as fibrinolysis dissolves these clots during healing. 

However, the elevated levels of alpha(2)-antiplasmin detected in the blood of long-haulers blocks fibrinolysis, causing blood clots to accumulate.

For now, the researchers are broadening the scope of their study to investigate whether administering blood-thinners to support the elimination of 'microclots' could help address the health issues faced by COVID long-haulers.