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COVID-19 and thrombosis: Separating facts from fiction

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With an extraordinary burden of thrombosis being observed among COVID-19 patients, Professor Roopen Arya, India spokesperson, World Thrombosis Day and Professor of Thrombosis and Haemostasis, King’s College Hospital, London busts some myths related to the link between COVID-19 and blood clots

Right at the beginning of the pandemic, studies from China showed that many hospitalised patients with COVID-19 had ‘sticky blood.’ SARS-CoV-2 infection can set off a harmful inflammatory response that affects blood clotting and damages blood vessels, termed thromboinflammation. This process is worse in those with severe disease and might take the form of pulmonary embolism in the lungs, deep vein thrombosis in the legs or less commonly thrombosis in the veins of the brain or gut. Arterial blood clots like heart attacks and strokes are also seen in COVID-19. About one in five of patients on critical care and one in 20 hospitalised patients develop pulmonary embolism. This is an extraordinary burden of thrombosis, never previously seen to this extent with any other infection.

Preventing thrombosis is an important part of caring for COVID-19 patients, particularly those with severe illness who have been admitted to hospital. Blood thinners or anticoagulants help prevent many of the clots. Low molecular weight heparin is usually the anticoagulant of choice in hospital, but COVID-19 has thrown up challenges as the standard preventive dose seemed less effective than usual, particularly in critical care.

As a result, higher doses of heparin started to be used but this can potentially cause more bleeding. We are fortunate that researchers all over the world have pulled together like never before and research has been accelerated, helping find answers that have swiftly impacted patient care. Many of these studies have looked at anticoagulants at various doses both in ward patients and those on critical care and also after discharge from the hospital.

We now know for instance that the use of full doses of anticoagulants in critical care patients without blood clots is not a good thing and can cause harm. The value of higher doses of anticoagulants in ward patients earlier in the illness is not certain as studies have shown either a small benefit or no benefit. Another common practice is that of sending patients home on anticoagulants. The current evidence does not support doing this routinely but it is possible that such an approach might be useful in selected patients. The role of anti-platelet drugs like aspirin is also being studied. Platelets in COVID-19 are sticky, increasing the risk of blood clots, and the use of anti-platelet drugs like aspirin is common in hospitalised COVID-19 patients in India. Recently, the UK study group who first showed the benefit of steroids reported that aspirin use in hospitalised COVID-19 patients is not helpful.

In addition to testing for COVID-19, labs in India are busy testing for many aspects of inflammation and blood clotting. The value of such costly tests in the majority of patients who are mildly affected or even without symptoms is very limited. D-dimer tests have been especially popular. It is the smallest fragment of a blood clot and can be raised in the presence of blood clots or inflammation. These are commonly raised in COVID-19 (as well as many other illnesses) and are being widely misused.

On the basis of abnormal results, even mildly-affected patients are being given anticoagulants which can increase the risk of bleeding. This is in addition to several other drugs at considerable cost, with every potential for harm. There is no evidence to support the polypharmacy being given to mildly-affected patients at home that seems to include steroids, antibiotics, ivermectin, anticoagulants, aspirin and even remdesivir infusions.

It is a big challenge in COVID times to stick to the evidence but we must do so as much as possible. There are 400 scientific papers related to COVID-19 published on a daily basis and only a handful of these will be relevant to clinical practice. We are accustomed to changing practice after months or years of deliberation and studying in-depth published papers that have been reviewed by experts. At times, in the past year, major changes in practice have been mooted on the basis of tweeted results or even press releases, it truly is a brave new world! Many treatments such as hydroxychloroquine, azithromycin and convalescent plasma have also fallen by the wayside as large studies failed to show benefit. New treatments continue to emerge and just this week we have had the encouraging news that the Regeneron monoclonal antibody cocktail reduces deaths in hospitalised COVID-19 patients who have an insufficient immune response of their own.

There is little doubt that just over a year on from when this all started, that we have a much better understanding of how to manage COVID-19. Ninety per cent of infected individuals will be mildly affected and should isolate at home, take rest and use paracetamol which will help with fever and aches. In those severe enough to be hospitalised and needing some form of respiratory support, incremental changes have made the difference, whether it is nursing patients on their front, better fluid management or use of medicines with anti-inflammatory and anti-viral effects such as steroids and remdesivir. To prevent blood clots in hospitalised patients, the judicious use of the right anticoagulant at the right dose at the right time is also an essential intervention.

Ultimately, prevention of SARS-CoV-2 infection is the best strategy, and as case numbers decline after the second wave in India, mass vaccination is the only way out of the COVID chakravyuha.

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