Stability of vitamin K antagonist anticoagulation after COVID‐19 diagnosis

Abstract Background Coagulopathy has been reported in severely ill patients with coronavirus disease 2019 (COVID‐19). It is unclear whether outpatients with COVID‐19 who are treated with vitamin K antagonists (VKAs) have unstable anticoagulation. Objective To assess the stability of VKA therapy in patients with COVID‐19 through a case‐crossover study. Methods Between February and July 2020, we included patients who tested positive for COVID‐19 from two anticoagulant clinics in the Netherlands. We collected international normalized ratios (INRs) determined between 26 weeks before infection and 12 weeks after. Time in therapeutic range (TTR) and the variance growth rate (VGR) were calculated within patients. Results Fifty‐one patients with COVID‐19 (mean age, 84 years) were included, of whom 15 (29%) were men. Mean TTR in the 26 weeks before COVID‐19 was 80% (95% confidence interval [CI], 75‐85) compared to 59% (95% CI, 51‐68) in the 6 weeks after infection. Mean TTR difference was −23% (95% CI, −32 to −14) with a time above therapeutic range of 38% (95% CI, 30‐47) in the 6 weeks after infection. The TTR rose again to 79% (95% CI, 69‐89) between 6 and 12 weeks after infection. Also, VGR increased, with a mean increase of 4.8 (95% CI, 2.1‐7.5) in the 6 weeks after infection. In the 26 weeks before infection, we registered 19 of 641 (3%) of INR ≥5.0 compared with 35 of 247 (14%) in the 6 weeks after (risk ratio, 4.4; 95% CI, 2.7‐7.3). Conclusions COVID‐19 is associated with a strong decrease in TTR and in therapeutic stability in patients taking VKAs. Additional monitoring in these patients is advised to maximize therapeutic stability.