Impact of Reduced INR Monitoring Frequency on Anticoagulation Control during the COVID-19 Pandemic: A Dutch Dynamic Cohort Study

Background Regular international normalized ratio (INR) monitoring is essential for maintaining optimal anticoagulation intensity in vitamin K antagonist (VKA)-treated patients. Unforeseen circumstances, such as the COVID-19 pandemic, led to temporary adjustments in anticoagulation clinic protocols, potentially reducing INR testing frequency and affecting INR control. We evaluated whether these adjustments resulted in increased INR intervals and affected INR control. Methods All patients managed by four Dutch Anticoagulation services were included in a dynamic cohort (December 2018 to December 2020). The study was divided into eight quartiles, with eligibility assessed at the start of each quartile. INR return interval and INR control (time under/in/above the therapeutic range, INR variability, mean INR and proportion of high INR values) were calculated per quartile. Pandemic quartiles were compared with corresponding calendar quartiles from the previous year to account for seasonal variation. Results Over 23,000 patients were included per quartile (mean age 80 years, 55% male). In each quartile, 52.7-56.0% of the patients maintained therapeutic range (TTR) above 70%. INR return interval increased during the pandemic, especially at the start (28.0 [IQR 19.3-38.5] vs. 25.1 [IQR 16.3-32.7] days, p-value < 0.001). No decrease in TTR was observed. Instead, a statistically significant but clinically modest increase occurred (72.8 [IQR 51.1-100.0] vs. 75.0 [IQR 54.4-100.0], p-value <0.01). Other INR control measures showed similar stability. Conclusion Compared with the pre-pandemic period, INR testing frequency decreased during the COVID-19 pandemic due to temporary protocol adjustments. INR control was not negatively affected. VKA therapy stability was maintained despite a 16% reduction in monthly INR measurements.