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We conducted a retrospective chart review of all PCR-positive COVID-19 patients age 60 or older who were admitted to a hospital within the health system. We chose to focus on patients 60 and older as they are at increased risk for severe COVID-19 and in an effort to reduce the variability between control and study groups. In order to assess 21-day mortality, all patients in the study had a SARS-CoV-2 RNA PCR performed before April 22, 2020 (n = 1,132). Mortality was assessed from the date of the first RNA PCR test undertaken during hospitalization, even if that first test was negative. If a later RNA PCR test demonstrated disease, we assumed the first test to be falsely negative (18) and a better marker of illness onset compared with the date of eventual positive RNA-PCR result. Those who had history of oral anticoagulation therapy with either a direct oral anticoagulant (DOAC) (apixaban, rivaroxaban, dabigatran) or warfarin were separated from the control group. Data retrieval could not differentiate between patients on oral anticoagulation prior to infection compared with those prescribed oral anticoagulation during hospitalization for COVID-19. Therefore, a chart review of all patients with exposure to oral anticoagulation was performed (n = 238) (Fig. Fig.11).

Patient inclusion & exclusion flow chart. COVID-19 = coronavirus disease 2019, ED = emergency department.

There were exclusions from chart review (n = 106): patients who were hospitalized for noninfectious conditions just prior to COVID-19 infection were excluded (n = 2, 0 deaths). Patients who were briefly started on oral anticoagulation during their hospital course but then had the anticoagulation discontinued due to a complication were also excluded (n = 7, 0 deaths). Patients who were not chronically on oral anticoagulation with a DOAC or warfarin but were discharged or expired while taking an oral anticoagulant during the course of hospital admission for COVID-19 were also excluded from the analysis (n = 93; eight deaths). Four patients not otherwise mentioned above were also excluded because they did not meet inclusion criteria for either the study groups or the control group: one patient that was on fondaparinux at the time of admission (alive); another patient that was not initially on anticoagulation but discharged on enoxaparin (alive); a patient previously prescribed warfarin but clearly identified as nonadherent with medication and with subtherapeutic international normalized ratio (INR) upon diagnosis of COVID-19 (deceased); and one patient whose chart review had conflicting documentation of whether they were on apixaban or warfarin (deceased). Of note, if the chart did not explicitly mention lack of compliance even if blood testing revealed a subtherapeutic anticoagulant effect at the time of admission, the patient was included in the appropriate group.

Ultimately, the final analysis included three comparison groups. The study groups include patients that were on a DOAC (n = 104) and patients on warfarin (n = 28). The control group included people with no exposure to oral anticoagulation prior to or during their hospital course (n = 894). Because the focus of this analysis is oral anticoagulation, we did not exclude patients on varying doses of heparin in the control group. During the study period, our health system’s practice for the treatment of all COVID-19 patients incorporated a protocol for varying doses of heparin/low-molecular-weight heparin based on level of d-dimer and clinical evidence of thromboembolism. (Specifically, if d-dimer < 5 mg/L prophylactic doses were given, if d-dimer > 5 mg/L intermediate doses were given and if confirmed thromboembolic process, therapeutic doses were given.) We assumed that other than the continuation of their baseline oral anticoagulant, patients in all three groups received similar care based on system-wide protocols for COVID-19 treatment, which remained unchanged with regards to anticoagulant use during the study period (those with oxygen < 94% were treated with hydroxychloroquine and tocilizumab; the critically ill were additionally treated with methylprednisolone and some with convalescent plasma).

We searched the electronic medical record for the primary outcome of all-cause mortality for the two study groups and the control group. Outcome was assessed at 21 days from the date of the first order for a COVID-19 RNA-PCR test. As a secondary outcome, bleeding events were reviewed and accounted for using International Classification of Diseases, 10th Revision (ICD-10) codes that include major bleeding events.

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