Clotting After COVID — Risk Spikes Early, Lingers 1 Year+

A potential reason to delay thrombogenic procedures

What’s the Claim?

Patients who have COVID appear to be at substantially increased risk of clotting events, both arterial and venous, in the weeks immediately after getting the virus (hazard ratio of over 30 for venous thromboembolism, with tight 95% CIs, 1 week after COVID diagnosis!). Some risk seems to persist for 1 year (with a hazard ratio 1.8, and the low end of the 95% CI still showing a 50% increased risk at 1 year compared to patients who did not have COVID). The risk is even more severe among patients hospitalized for COVID.

How’s It Stack Up?

Other studies have suggested that thromboembolic risk increases with a diagnosis of COVID, but this is one of the largest and most-comprehensive studies out there. We lack guidelines on this important topic. It seems likely they'll be forthcoming.

What’s Our Take?

This is potentially practice changing. Based on these findings, one might want to delay potentially thrombogenic procedures (such as hip/knee arthroplasty) for as long as is practicable, especially in patients who were hospitalized for COVID, and perhaps using more-aggressive thromboprophylaxis if a delay is not possible or if the patient has other risk factors for clotting. It raises the question of whether it's worth delaying a couple months even for smaller orthopaedic procedures on the lower extremity where there is some risk of clots – such as knee scopes and the like — and whether one should use thromboprophylaxis in patients undergoing those procedures who have risk factors for clotting.


Knight R, Walker V, Ip S, et al. Association of COVID-19 With Major Arterial and Venous Thrombotic Diseases: A Population-Wide Cohort Study of 48 Million Adults in England and Wales. Circulation. 2022;146:892-906.