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COVID-19 associated with higher VTE rates relative to influenza

Presented by
Dr Milou Stals, Leiden University Medical Centre, the Netherlands
ISTH 2020


COVID-19 patients showed much higher rates of thrombotic complications compared with influenza patients. Dutch study results suggest this may be due to possible specific effects of SARS-CoV-2 on the coagulation system.

“An activation of blood coagulation was already announced in the first studies on COVID-19 patients at the beginning of this year,” stated Dr Milou Stals (Leiden University Medical Centre, the Netherlands) [1]. Up to about 50% COVID-19 patients in ICU sustain thrombotic complications, with 87% of them experiencing pulmonary embolism and 7% ischaemic stroke [2,3]. In general-ward patients, the incidence is suggested to be 5-10 % [3,4].

The presented retrospective cohort study aimed to compare the cumulative incidence of thrombotic events of hospitalised COVID-19 patients and hospitalised influenza patients [1]. These results intended to clarify whether thrombotic complications are prompted through the presence of conventional risk factors or a specific, SARS-CoV-2-associated pro-coagulative effect. Besides incidence of venous thromboembolism (VTE) and arterial thromboembolism in COVID-19 versus influenza patients, the study also looked at a potential link between pre-existing anticoagulation treatment at admission and later thrombosis during hospitalisation.

The study included data on COVID-19 patients (n=579) hospitalised at 3 Dutch hospitals between 24 February and 25 April 2020. All patients were treated with thrombosis prophylaxis but investigations for VTE were only performed in case of clinical suspicion. Data on the included influenza patients (n=27,980) were obtained from the Statistics Netherlands database. As this data did not allow for discrimination between general-ward and ICU patients, comparisons were only possible for VTE incidence rates of all hospitalised influenza patients. Cumulative incidences of VTE were calculated with Kaplan-Meier analysis for the COVID-19 patients only. Baseline characteristics within the COVID-19 group showed a mean age of 67, 66% males, and 13% of long-term anticoagulated patients at admission.

After adjustment for the competing risk of death, the cumulative 30-day incidence of VTE and arterial thromboembolism together in the COVID-19 group was 19.6% for general-ward plus ICU patients, with 5.3% incidence on the general ward and 34.1% on ICU. Looking at VTE alone, the respective incidences were: 17.8%, 3.8%, and 32.5%. There was a large difference with the influenza group, which showed a VTE incidence of only 1.04% in hospitalised patients. As for long-term anticoagulant treatment at hospital admission, this led to a lower risk of thrombotic complications in general (HR 0.09) and especially in VTE (HR 0.04).

Dr Stals concluded that the much higher incidence of thrombotic complications in COVID-19 patients implies a specific effect of SARS-CoV-2 on coagulation, which is currently under further investigation in the Netherlands.

    1. Stals MAM, et al. LB/CO01.4, ISTH Virtual Congress 2020, 12-14 July.

    2. Klok FA, et al. Thromb Res. 2020;191:148-150.

    3. Middeldorp S, et al. J Thromb Haemost. 2020;18(8):1995-2002.

    4. Lodigiani C, et al. Thromb Res. 2020;191:9-14.


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