question: BACKGROUND: Numerous studies have documented reduced access to patient care due to the COVID-19 pandemic including access to a diagnostic or screening tests, prescription medications, and treatment for an ongoing condition. In the context of clinical management for venous thromboembolism, this could result in suboptimal therapy with warfarin. We aimed to determine the impact of the pandemic on utilization of International normalized ratio (INR) testing and the percentage of high and low results. METHODS: INR data from 11 institutions were extracted to compare testing volume and the percentage of INR results &#8805;3.5 and &#8804;1.5 between a pre-pandemic period (January-June 2019, period 1) and a portion of the COVID-19 pandemic period (January-June 2020, period 2). The analysis was performed for inpatient and outpatient cohorts. RESULTS: Testing volumes showed relatively little change in January and February, followed by a significant decrease in March, April and May, and then returned to baseline in June. Outpatient testing showed a larger percentage decrease in testing volume compared to inpatient testing. At 10 of the 11 study sites we observed an increase in the percentage of abnormal high INR results as test volumes decreased, primarily among outpatients. CONCLUSION: The COVID-19 pandemic impacted INR testing among outpatients which may be attributable to several factors. Increased supratherapeutic INR results during the pandemic period when there was reduced laboratory utilization and access to care is concerning because of the risk of adverse bleeding events in this group of patients. This could be mitigated in the future by offering drive through testing and/or widespread implementation of home INR monitoring.