Patients admitted to hospital with COVID-19 already taking oral anticoagulant medication may be less likely to end up being admitted to intensive care, a large UK study has found.

While there was no difference in mortality between those who were on anticoagulants and those who weren’t in the analysis of 5,883 patients, the study also found that patients on anticoagulants prior to admission showed a reduced inflammatory response.

It is the largest to date looking at mortality, thrombosis, major bleeding, multi-organ failure and admission to ICU covering 26 UK hospitals in between April and July 2020.

In total, 16.4% of patients were taking oral anticoagulation medication at the time of admission. Overall mortality at 90 days was 29.2% with an incidence of thrombosis in admitted patients of 5.4%, major bleeding 1.7% (of which 36.4% were fatal) and multi-organ failure 3.3%.

Patients who had thrombosis had a 1.8-fold increased risk of dying. Major bleeding and multi-organ failure were associated with a 4.5 and 5.9-fold increased chance of death respectively.

The initial crude data showed death in hospital was higher amongst patients already taking anticoagulants at the time of admission, with 35.9% (346/963) of patients already on oral anticoagulants dying, compared with 27.9% (1,373/4,920) of patients not on oral anticoagulants before they were hospitalised with COVID-19.

Writing in The British Journal of Haematology, the researchers noted they expected this due to the underlying comorbidities and age in those patients who would have been prescribed the drugs.

But after an adjusted multivariate analysis there was no difference in mortality rates between the two groups, they concluded.

The only aspect that remained significant was admission to intensive care with a hazard ratio of 1.98 in those not taking anticoagulation medication before their hospitalisation.

The unadjusted results also showed that risk for thrombosis and multi-organ failure were lower for patients on oral anticoagulants which was “slightly surprising given the increase in mortality”.

Those differences did not remain statistically significant in the adjusted analyses but “suggests that patients with identifiable risk factors may benefit from therapeutic anticoagulation, a question currently being studied in large platform trials”, the researchers concluded.

It highlights the “fine balance” between prevention of thrombosis and avoiding major bleeding and emphasises the need for the correct anticoagulant regimen in these patients, they said.

“Patients taking oral anticoagulants may therefore benefit from earlier anticoagulation but are frequently using anticoagulation for cardiovascular disorders which are themselves associated with poor outcomes from COVID-19.

“Moreover, these patients would require continuation of anticoagulation throughout their admission whilst the adaptive studies showed that for severely ill patients requiring organ support, therapeutic anticoagulation was associated with poorer outcomes associated with an excess of bleeding.

“Consequently, the balance of risk and benefit for these patients is unclear.”