Ascertainment and validation of major bleeding events in a primary care database

The purpose of the study is to evaluate the impact of validation on the identification of major bleeding events in The Health Improvement Network (THIN) database in patients receiving anticoagulant therapy.

Patients aged 2 to 89 years with a first prescription for an anticoagulant (rivaroxaban or warfarin) between 2012 and 2015 were identified in THIN. Major bleeding events, defined as bleeding events necessitating hospitalization or referral to accident and emergency services or a specialist clinic, were identified using a 2-step ascertainment process based on read codes only, and then validated using a 2-step process requiring manual review of patients' records.

The positive predictive value for the ascertainment of major intracranial (IC) bleeds using only read codes was 96.9%, compared with 70.4% for gastrointestinal (GI) bleeds and 64.1% for urogenital (UG) bleeds. The incidence rate of major IC bleeding events was therefore similar when it was calculated before and after validation (0.32 per 100 person-years and 0.31 per 100 person-years, respectively). The incidence rate of major GI bleeds identified using read codes alone was reduced following validation from 2.05 to 0.94 per 100 person-years, and that of major UG bleeds decreased from 2.45 to 1.11 per 100 person-years.

Major GI and UG bleeding events ascertained from THIN using read codes require validation using additional information to prevent outcome misclassification. The absence of validation may lead to overestimated incidence rates of major bleeding for GI and UG bleeds.