Risk factors for venous thrombosis after discharge from medical hospitalizations: the Medical Inpatient Thrombosis and Hemostasis study

BACKGROUND: Many studies on hospital-associated venous thromboembolism (VTE) do not specifically assess the risk factors for events after discharge. OBJECTIVES: This study aimed to identify risk factors for postdischarge venous thromboembolism (PD-VTE) after a medical hospitalization. METHODS: Patients discharged from a medical hospitalization at the University of Vermont Medical Center between January 2010 and September 2019 were followed up for inpatient and outpatient VTE events for up to 90 days. Age-adjusted, sex-adjusted, race-adjusted, and length of stay-adjusted Cox models estimated the hazard ratios (HR) and 95% CIs for potential risk factors for PD-VTE. RESULTS: Among 22 599 admissions, there were 180 PD-VTE events (90-day cumulative incidence of 0.8%). The median time from discharge to PD-VTE was 29 days. Of previously identified in-hospital VTE risk factors, only history of VTE (HR, 3.34; 95% CI, 2.26-4.93) and active cancer (HR, 3.13; 95% CI, 2.31-4.23) were associated with increased risk of PD-VTE. Compared to <2-day hospital stays, longer hospital stays (HR, 1.84; 95% CI, 1.23-2.75, for 6-10 days and HR, 1.64; 95% CI, 0.93, 2.90, for 11+ days) were associated with increased risk of PD-VTE. Both mortality (HR, 1.22; 95% CI, 1.06-1.41 per SD higher) and readmission (HR, 1.30; 95% CI, 1.13-1.50, per SD higher) Elixhauser comorbidity indices were associated with increased risk of PD-VTE. CONCLUSIONS: Risk factors for VTE after discharge from medical hospitalization differ from risk factors for in-hospital VTE. These data support that characteristics of the hospitalization influence PD-VTE risk, and if indicated, PD-VTE risk should be assessed at discharge.