Background: Patients on warfarin require regular international normalized ratio (INR) monitoring. The SARS-CoV-2 pandemic may have substantially affected in-person medical visits and laboratory testing. However, it is not clear how warfarin monitoring practices have been affected by the pandemic, given the importance of tight INR control.

Aims: To assess whether chronic warfarin management, as measured by INR testing frequency and time in therapeutic range (TTR), differed during the COVID-19 pandemic compared with the pre-pandemic period.

Methods: We identified all patients enrolled in an anticoagulation clinic associated with an urban academic medical between January 1, 2019 and May 31, 2021 with at least 2 INRs checked during this time period. We calculated frequency of INRs checked per month and TTR based on individual INR goals and compared the pre-pandemic (Jan 2019-Feb 2020) and pandemic (March 2020-May 2021) periods. INR frequency and TTR were modeled as a function of time period using Poisson and linear regressions respectively, accounting for repeated observations.

Results: Of the 1052 patients included, 43.9% were women and average age was 66.3 years. Pre-pandemic, an average of 1.58 (95% CI 1.52-1.64) INRs were checked per month, as compared with 1.09 (95% CI 1.03-1.15) in the pandemic period (p < 0.001) (Figure 1). Average TTR per month was also calculated (Figure 2). On average, TTR was 56.8% (95% CI 54.9-58.8%) pre-pandemic compared to 39.4% (95% CI 37.5-41.5%) during the pandemic period (p < 0.001).

Conclusion(s): There was a significant decrease in the frequency of INR measurements as well as TTR during the pandemic. A number of factors may have contributed to this, including regulatory and logistical constraints on clinic and laboratory visits and patient anxiety about visiting medical facilities. Larger scale studies are warranted to further characterize pandemic effects on warfarin use and monitoring, as well as clinically significant outcomes of thrombosis and hemorrhage.

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Figure 1: Average INR frequency plotted by month from 1/1/19 to 5/31/21. Dashed horizontal line represents three-month moving average. Dashed vertical line at March 2020 represents the end of the “pre-pandemic” period and beginning of the “pandemic” period.

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Figure 2: Average time in therapeutic range -TTR- plotted by month from 1/1/19 to 5/31/21. Dashed vertical line at March 2020 represents the end of the “pre-pandemic” period and beginning of the “pandemic” period.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/impact-of-the-covid-19-pandemic-on-anticoagulation-control-for-patients-using-warfarin/