World Thrombosis Day: what is the relationship between Covid-19, deep vein thrombosis and pulmonary embolism?

Blood clotting (or thrombosis) is a major lifesaving feature of our physiology, and at the same time life threatening; sticky blood caused by Covid-19 has highlighted the mostly unspoken ongoing impact of blood clots on worldwide health.

GM Journal interviewed Prof Beverley Hunt, OBE – who is a Professor of Thrombosis and Haemostasis at King’s College London and is a co-founder and Medical Director of Thrombosis UK – about current issues, developments, and awareness campaigns that are central to this year’s World Thrombosis Day’s message.

One in four people will die from a thrombosis (blood clot being the colloquial), while most people will be familiar with the causes and symptoms of stroke or a heart attack, the symptoms and causes of a deep vein thrombosis or of a pulmonary embolism are still little understood by the general public.
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The overlooked clots: deep vein thrombosis and pulmonary embolism

Deep vein thrombosis (DVT) is a serious condition that occurs when a blood clot, a solidified clump of blood, forms in a vein deep within the body, usually the leg. Prof Hunt explained that one initial symptoms of DVT, for 20% of people, is that the restricted blood flow causes blue or red marks and/or swelling in the affected area.

Although she said that a much more common symptom is pain – “when we are talking about pain, we are talking about that you have just pulled a muscle”. However, even more worrying for some people “the DVT is totally clinically silent, you don’t get any symptoms at all, the first sign that anything is wrong is when part of the clot has broken off and travelled around the body and blocked some of the pulmonary arteries” – a pulmonary embolism (PE), or a blood clot that occurs in the lungs.

Prof Hunt explained that signs of a PE can be subtle, while text book symptoms include chest pains, struggling to breath, or coughing up blood, though it is often forgotten tiny clots can happen over a period of time so people might have only noticed a recent cough. But if left unnoticed or untreated, life threatening damage will be caused to the lungs due to restricted blood flow and consequentially lack of oxygen.

Through her work with Thrombosis UK from 2010, NHS England has mandated DVT risk assessments for all incoming adult patients “so, if you go to hospital you will automatically be assessed for your risk from blood clots, and get blood thinners, stockings, or intermittent pneumatic compression if you have a risk”.

“The high-risk factors for having clots are really immobility, and I think everybody in the UK understands that if you go on a long-haul flights you have an increased risk of a blood clot – and that’s all about immobility – and make sure that you don’t get dehydrated”. Asides from lifestyle, Prof Hunt said that physiological high-risk factors include obesity, female hormones, cancer, surgery, and age – particularly over 70.

Covid-19, sticky blood, and thrombosis

Around 5% of Covid-19 patients (around day 7-10 of the infection) develop Covid pneumonia – which has particular relevance to the flow of blood and the rates of thrombosis in hospitals. During Covid pneumonia “the patient has an amazing inflammatory response to the pneumonia in the lungs, and the lymphocytes and the macrophages go ape, and they produce a lot of cytokines which tell the liver to produce an increased level of coagulation proteins. So, people who have Covid pneumonia have really sticky blood – incredibly sticky blood”.

“So if we talk about the main coagulation protein which is fibrinogen, it is normally present in about 2-4 grams per litre, and looking at our patients – the average level of fibrinogen in intensive care patients was 8 – that’s double – that’s extraordinary for the protein to double, and we have had levels as high as 14.”

“And the other thing that Covid does, is that it infects the endothelium, the lining of the blood vessels, and activates them, and makes them switch – from telling the blood that flows over it to not clot, to actually promoting clots.”

Prof Hunt emphasised that this scenario is limited to those in intensive care and would not affect the majority of Covid-19 patients. But for those who are self-isolating she highly recommended the need to keep mobile to prevent clotting, as the blood flow to the veins in your legs is reliant on movement.

Although those who are sent to intensive care are severely at risk from blood clots: from the sticky blood caused by the immune response, and from remaining immobile due to ventilation – as well as being combined with the Covid-19 intensive care profile of older or obese patients. This is why “everybody who is coming into hospital with Covid in this country and internationally is being given small doses of anticoagulants, and the big question at the moment is should we be giving more thromboprophylaxis than we would normally give to a patient who is on a ward or who’s on a ventilator”.

World Thrombosis Day

Prof Hunt said that currently NHS England leads the world in reducing deaths from PE, with World Thrombosis Day working, prior to the pandemic, with the World Health Organization to promote the DVT risk assessments worldwide. Due to its toxic affiliation with Covid-19, thrombosis’s public image has been separated from being merely heart attacks and stroke. The aim now for World Thrombosis Day is the further promotion of awareness for DVT, PE, and others such as venous thromboembolism.

“A lot of healthcare professionals and the public have woken up to DVT and PE; when before it wasn’t so sexy, now it really is a big issue with Covid patients, so it’s a real eyeopener for a lot of people.”