Adult patients ≥18 years of age admitted into a hospital ED with a primary discharge International Classification of Diseases (ICD)-9 or ICD-10 diagnosis code of venous thromboembolism (VTE) were identified from the Premier Hospital database from August 1, 2014 through May 31, 2018. Patients who received apixaban or warfarin during the ED visit were selected and grouped into two study cohorts according to the OAC received. Patients treated with warfarin were additionally required to have received ≥1 injectable anticoagulant, including LMWH, UFH, or fondaparinux, during ED admissions. The first of such VTE ED admissions was defined as the index event, with the corresponding ED or hospital discharge date as the index date. Patients who received both apixaban and warfarin or any other DOAC (rivaroxaban, dabigatran, edoxaban, betrixaban) during their index ED admission, or were diagnosed with atrial fibrillation/atrial flutter or pregnancy during the 12-month baseline period prior to the index event or during the index event, or had inferior vena cava filter usage during the baseline period or index event, or were transferred from other facilities, or died during the index event were excluded from the study population.
Patients must have met all the following inclusion criteria to be eligible for inclusion in the study:
• Have a primary diagnosis of VTE identified by the following ICD-9-CM or ICD-10 codes from the Premier Hospital database between August 1, 2014 and May 31, 2018
o Pulmonary embolism (PE)
o Deep vein thrombosis (DVT)
• Received either apixaban or warfarin prior to discharge from the ED
o Patients receiving warfarin were further required to have received at least one of the injectable anticoagulants, including LMWH, UFH, or fondaparinux, during their ED admission.
• Have an age ≥18 years as of the index ED admission for VTE
Patients meeting any of the following criteria were not included in the study:
• Received both apixaban and warfarin during the index ED admission. This exclusion criterion allowed for a clean grouping of patients into the apixaban and warfarin cohorts.
• Received any other DOAC, including rivaroxaban, dabigatran edoxaban and betrixaban, during the index ED admissions.
• Had medical claims indicating one of the following conditions or procedures during the index ED admission or within 12 months prior to the index date:
1. Atrial fibrillation (AF)/ Atrial flutter (AFL)
2. Pregnancy
3. Inferior vena cava filter (IVCF) usage:
• Patients transferred from other facilities.
• Patients who died during the index ED admission.