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Blood clots in lungs may be major cause of COVID-19 death

Date: 25 May 2020 Tags: Miscellaneous


Research has shown that it is not the pneumonia itself, but rather it is early and progressive clotting of blood in the lungs (pulmonary thrombosis) which impairs blood supply and gas exchange leading to respiratory failure and death. This mechanism is supported by several levels of evidence.



The major fear of COVID-19 infection is the significant fatality associated with it. Even though death from this infection has been relatively low in India but given the very large number of people infected, significant numbers continue to die.



  • It has been recognised from the very early reports that very high proportions of patients with COVID-19 infection presenting to hospitals had elevated levels of d-dimer, a general marker of thrombosis in blood vessels.

  • Those with highly elevated d-dimer levels were more prone to severe respiratory complications and death. In most of these patients, there are no other sites of thrombosis to explain the raised d-dimer such as the leg veins which is much more common but has only been reported in a few patients.

  • The strongest evidence for this extensive microvascular thrombosis comes from several autopsy studies from different countries.

  • All these have shown extensive blood clots in the small vessels of the lung (microvascular thrombosis - MVT) with only modest evidence of the pneumonia suggesting that it is the blood clots which cause poor oxygenation and respiratory failure.

  • It is also known now that the receptors on the cells in the air-pockets of the lung which allow entry to the COVID-19 virus into those cells, are shared by the endothelial cells which line the blood vessels of the lung.

  • Autopsy studies have confirmed distinct infection in these cells which then trigger blood clotting in the small blood vessels. If not controlled immediately, this rapidly extends and leads to treatment unresponsive respiratory failure.

  • The manifestation of ‘silent pneumonia’ or ‘silent hypoxia’ that is being increasingly recognised even in the lay media where relatively well-looking people have low blood oxygen and then suddenly collapse, most likely due to extending pulmonary thrombosis.

  • It is important therefore that the public as well as health care professionals be aware of this problem of blood clots in the lung whose severity is unique to COVID -19.

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