- Prof. Beverley Hunt explains why blood clots are dangerous for those with COVID-19.
- A significant number of people with severe COVID-19 develop life-threatening clotting.
- They are changes in the flow of the blood, changes in the stickiness of the blood.
- Chemical cytokines tell the liver to make more clotting proteins.
- The blood is full of clotting proteins that make it very sticky and very ready to clot.
- The clotting factors switch soluble fibrinogen to insoluble fibrin.
According to an article published in Medical News Today, COVID-19 leads to blood clots in a significant number of people who have a severe form of the disease.
Why blood clots are dangerous?
In an interview, thrombosis expert Prof. Beverley Hunt explains why blood clots are dangerous for those with the new coronavirus.
As news of a SARS-CoV-2, the new coronavirus, traveled across the globe, many experts thought that they would primarily encounter respiratory symptoms.
And little did we expect to be hearing about cardiovascular complications, digestive symptoms, the loss of smell and taste, and the likes of “COVID toe,” one of a collection of skin symptoms that some people with COVID-19 develop.
Blood clots are another complication that has been making headlines. MNT reported on a series of articles in the journal Radiology that suggested that a significant number of people with severe COVID-19 develop life-threatening clotting.
How patients are at risk?
But why would a virus that primarily infects the respiratory tract cause blood clots? And how is this putting patients at serious risk?
Prof. Beverley Hunt is the medical director of the British charity Thrombosis UK, as well as chair of the steering group for World Thrombosis Day. She is a professor of thrombosis and hemostasis and works for the United Kingdom’s National Health Service (NHS) in London.
Prof. Hunt told MNT about the biology of blood clotting, her surprise at how the new coronavirus changes the properties of the blood in those with severe disease, and why we should keep moving, even during a lockdown, to reduce our risk of thrombosis.
The conductor of the blood clotting orchestra
MNT: How do blood clots form, and why are they potentially dangerous?
Prof. Hunt: In 1846, the German pathologist [Rudolf] Virchow described three things that predispose people to venous thrombosis.
They are changes in the flow of the blood, changes in the stickiness of the blood — although he didn’t use the word “sticky” then — and changes in the blood vessel wall.
Of these, probably the most important one for the average member of the public is flow. Just sitting here for 90 minutes without moving my legs, blood flow crashes. It drops by about 50%.
When you walk, every time your muscles contract, they squeeze the veins and push the blood back up toward the heart.
There isn’t a natural muscular system within the veins, unlike within the arteries. We’re totally dependent on movement to keep the flow going.
This is a major risk factor for hospital patients, for someone who is sick, but also for anyone sitting for long periods of time.
As far as the stickiness is concerned, we are talking about changes in the blood proteins. The commonest cause of these changes is being ill.
If you’re ill, you produce chemical cytokines that tell the liver to make more clotting proteins. Then your blood is full of clotting proteins that make it very sticky and very ready to clot.
The last thing is the lining of the blood vessel. It’s very susceptible to hormones, particularly in people who are ill and people who take hormone replacement therapy. Those cytokines make it much, much more liable to form a clot.
When we come to COVID-19, we know that the new coronavirus can enter the lining of the blood vessels. The new coronavirus behaves in some way like the conductor of the blood clotting orchestra.
‘I’ve never seen such sticky blood’
MNT: Were you expecting to see such a big problem with blood clots in people with COVID-19?
Prof. Hunt: The issue with COVID-19 is that the blood is incredibly sticky.
We are seeing people in hospital with pneumonia. They are in hospital because they are short of oxygen, and they need extra oxygen. That’s really why they are coming in.
We know that most people who get COVID-19 get better in about 7–10 days, and we have about 5% who develop pneumonia.
Their immune system is reacting very strongly to pneumonia, and the lungs are full of immune cells that produce cytokines. In turn, these tell the liver to make clotting proteins. The inflammatory mechanism leads to what we call a “prothrombotic state.”
Let me give you an example. The main clotting protein in the blood is fibrinogen. It’s soluble, and you have 2–4 grams per liter in your blood.
The clotting factors switch soluble fibrinogen to insoluble fibrin, and that is the clot.
The level is 2–4 grams per liter in most people. If you are pregnant, or as you get older, the levels get higher. They might go up to 5, 6, or even 7 [grams per liter].
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Source: MedicalNewsToday
