Covid-19 and blood clots: All you need to know

Clotting of blood is useful in an injury. But when the blood clots inside a blood vessel without injury, it can cause life-threatening complications

The world is battling coronavirus at the moment, which is known to affect different people in different ways. “Along with fever and lung fibrosis, even blood clotting may be seen in some patients,” said Dr Chetan Bhambure, consultant interventional cardiologist, Wockhardt Hospital, Mira Road.

Everything you need to know about blood clotting

Clotting of blood is useful in an injury. But if it clots inside a blood vessel without injury, it can cause life-threatening complications. The virus invades and damages endothelial cells, triggering the body’s clotting mechanism. The damage to the tissues around them due to viral infection or the body’s immune response causes increased clotting. An increase in inflammatory molecules that our immune system produces in response to viral infection can activate clotting. Various studies have suggested that the platelets of people hospitalised with COVID-19 were found to be hyperactive, having increased activation and aggregation (clumping), he explained.

Some people are at higher risk for developing clots. “These include hospitalised patients, patients with high blood levels of d-dimer (a marker for clotting), and comorbidities like heart disease, diabetes, and obesity. Thus, these patients need to be extra cautious if they contract the covid infection,” expressed Dr Bhambure.

Clotting can cause several complications like a heart attack if an artery of the heart gets blocked; stroke wherein an artery of the brain is blocked causing paralysis; pulmonary embolism wherein an artery in the lungs gets blocked causing a sudden drop in blood pressure and blood oxygen levels; limb ischemia which is a clot in the artery of legs; mesenteric ischemia that is a clot in the arteries supplying blood to the intestines; deep vein thrombosis wherein blood clots in the veins of the legs can result in pulmonary embolism; and cerebral venous sinus thrombosis which is clots in the veins of the brain.

What is a blood clot?

A blood clot is a clump of blood that has changed from a liquid to a gel-like or semisolid state. Clotting is a necessary process that can prevent you from losing too much blood in certain instances, such as when you’re injured or cut.

When a clot forms inside one of your veins, it won’t always dissolve on its own. This can be a very dangerous and even life-threatening situation.

An immobile blood clot generally won’t harm you, but there’s a chance that it could move and become dangerous. If a blood clot breaks free and travels through your veins to your heart and lungs, it can get stuck and prevent blood flow. This is a medical emergency.

You should call your doctor immediately if you think you might have a blood clot. A healthcare professional will be able to look at your symptoms and medical history and let you know what steps to take from there.

Blood clotting factors

First, COVID-19 can cause severe inflammation, which can trigger your clotting system.

“When you, say, fall and skin your knee, it turns your immune system on, and one of the ways your immune system reacts to an injury is by making your clotting system more active,” Exline said. “It kind of makes sense that your body would say, if I see an infection, I need to be ready to clot. But when the infection is as widespread and inflammatory as COVID-19, that tendency to clot can become dangerous.”

And when you’re sick with COVID-19 or following stay-at-home or quarantine orders, you probably aren’t moving much.

“If you’re immobile, you have an increased risk factor for blood clots,” Exline said.

Paired together, inflammation and immobility create a near perfect environment for blood clots in your legs and lungs, Exline said. Patients with severe cases of COVID-19 seem especially susceptible, as do those with other health risk factors such as cancer, obesity and a history of blood clots.

Blood clot treatment

Knowing this, health care providers have changed the way they treat COVID-19 patients to specifically address the risk of clotting. It’s taken quick, widespread collaboration. At the Wexner Medical Center, specialty practice pharmacists along with critical care medicine, cardiology, hematology, emergency medicine and internal medicine doctors developed guidelines on how to manage these patients, Blais said.

“We’ve done the amount of work that some people would take a year or two to put together in a matter of weeks,” she said.

Now, patients who are sick enough from COVID-19 to go to the hospital receive blood tests to gauge the activity of their clotting systems. Recent studies have demonstrated that patients with COVID-19 are prone to clotting, but patients in the ICU may also be at risk for bleeding.

"Health care providers must carefully weigh the risks and benefits of anticoagulation for each individual patient," Exline says.

Those whose clotting systems aren’t particularly active receive treatments to prevent clots such as compression socks, inflatable cushions for their calves or small injections of blood thinners. Those with more active clotting systems receive full doses of blood thinners if they’re not at a high bleeding risk.

“We’re having to be thoughtful about our approach with treatment, especially because there is limited data in COVID-19 patients,” said Tiffany Ortman, PharmD, a specialty practice pharmacist in outpatient care at the Ross Heart Hospital.

After patients leave the hospital, health care providers continue to monitor patients for clotting symptoms and lower their risk through medications. Some currently active research studies are attempting to understand how long patients should stay on anticoagulation medication as they recover from COVID-19.

Blood clots and COVID-19 vaccination

Recent news from both Europe and the United States has raised concerns about blood clots after COVID-19 vaccination. It's important to note that the most common vaccines in the U.S. — the Pfizer and Moderna vaccines — have not been found to have a high risk of blood clots.

Blood clots have been reported in Europe after the AstraZeneca vaccine and in the U.S. with the Johnson & Johnson vaccine, but these incidents have been extremely rare, Exline notes.

"There may be an extremely low risk of blood clots with one type of COVID-19 vaccine, but you're more at risk for injury driving to your vaccine appointment than from any side effect from the vaccine itself," Exline says. "It's important to remember that the risk of blood clots from a COVID-19 infection is much more likely than any side effect of a vaccine. If you want to protect yourself from blood clots, get vaccinated."

Who's most at risk for blood clots, and what to look for

While those with severe cases of COVID-19 appear to be more affected by blood clots, those who don’t come to the hospital could still be at risk, said Aaron Dush, PharmD, a specialty practice pharmacist at the James Cancer Hospital and Solove Research Institute.

They, as everyone, should monitor for signs of clots and possible stroke or heart attack: