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Post Discharge Risk of Venous Thromboembolism in a Primary Care Population

Introduction:
 Among all venous thromboembolism (VTE) events, 20% occur during or in the three months following a hospitalization. Inpatient VTE prevention strategies incorporate pharmacological interventions that do not commonly continue after discharge. Recent trials of post-discharge prophylaxis have not identified benefit among recently discharged patients, probably due to lack of understanding of the relative and absolute risks of VTE after discharge.
 In order to better clarify the scope of the problem, we quantified the risk of VTE during hospitalizations, and up to 3 months post-discharge relative to patients without a recent hospitalization.
 Methods:
 We followed all primary care patients aged ≥18, at the University of Vermont Medical Center's primary care clinics for hospitalization and VTE using the electronic medical record. Patients entered the cohort at their first contact with the health system after 06/30/2010 and were followed until their last contact, change of primary care provider to a non-University of Vermont provider, or December 2016, whichever occurred first. First VTE during follow-up was defined as having two outpatient VTE codes 7-185 days apart or one inpatient code. Patients with a VTE code in the first 3 months of enrollment were excluded as having pre-baseline VTE.
 Hospital-acquired VTE was defined as VTE occurring after day 1 of hospitalization (to correctly categorize people with an outpatient VTE and admitted with VTE) and post-discharge VTE was defined as VTE occurring during successive 1-month time periods after discharge from the hospital. Age- and sex-adjusted Cox proportional hazard models were used to calculate hazard ratios (HRs) of VTE during and after hospitalization. Hospitalization and time periods after hospitalization were modeled as time-varying covariates and included the time in the hospital, and 1-30 (month 1), 31-60 (month 2), and 61-90 (month 3) days post-discharge. The reference group for this analysis was outpatients who were not within 90 days of a hospitalization.
 Results:
 From 2010-16, 87,821 patients (49,468 women, 56%) were included, with a mean age of 46 years. With 371,429 person-years of follow-up (mean follow-up 4.2 years), 749 first VTE events occurred for a rate of 2.0 per 1,000 person-years. There were 57,837 hospitalizations among 21,963 individuals for a rate 155.7 hospitalizations per 1,000 person-years.
 The Table presents the person-years of follow-up, the number, rate, and age- and sex-adjusted hazard of VTE for hospitalization and successive months after hospitalization. The VTE rate was 1.5 per 1,000 person-years outpatients not within 3 months of hospitalization. During hospitalization, the rate was 75.9 per 1,000 person-years, and slowly decreased over time after discharge, but remained elevated at 5.0 per 1,000 person-years event in month 3 after discharge. The age- and sex-adjusted HR for VTE was 40.3 during hospitalization and declined to 18.1, 6.0 and 2.9 over successive 1-month intervals after discharge (Table).
 Conclusion:
 In a primary care population in northern Vermont, hospitalization and time periods after hospitalization were associated with a dramatically increased incidence of and risk for VTE compared with patients not hospitalized in the past 3 months. The rate of VTE (34.4 per 1,000 person-years) in the first month post-discharge might not warrant universal post-discharge VTE prophylaxis, but suggests that if we can identify high-risk patients at low risk for bleeding, pharmacologic VTE prophylaxis may be appropriate in some patients. Further study of risk factors for post-discharge VTE is warranted.
 Table
 
 
 No relevant conflicts of interest to declare.
