Continuity of care and medication adherence in patients with angina: a retrospective cohort study using Korea’s National Health Insurance data

Background Angina, a major manifestation of ischaemic heart disease, affects 3–7% of adults and is a leading cause of cardiovascular morbidity. As an ambulatory care-sensitive condition, its outcomes can be improved through proactive outpatient management. However, the real-world impact of continuity of care (COC) and medication adherence, measured by the medication possession ratio (MPR)—on angina complications in South Korea remains poorly understood.Objective This study evaluated the effectiveness of COC and MPR in patients with angina using comprehensive national data and examined the outcomes at the hospital level.Methods This retrospective cohort study used data from the National Health Insurance Service of Korea between 2002 and 2019. We identified 11 127 patients aged >30 years newly diagnosed with angina, applying strict exclusion criteria to ensure cohort validity. COC was categorised as high (COC index=1.0) or low (<1.0), and MPR was classified as excellent (≥80%), good (60%–79%) or poor (<60%). Complications, defined as the onset of coronary artery disease (International Classification of Diseases, 10th Revision: I20–I25), were analysed using Kaplan-Meier survival curves and Cox proportional hazards models, adjusting for key sociodemographic and clinical covariates.Results Among the study cohort (mean age 63.4 years; 54.3% female), 64.2% had low COC. While patients with low COC had a 20% higher risk of complications compared with those with high COC (HR: 1.20; 95% CI: 0.87 to 1.65; p=0.266), this was not statistically significant. Similarly, patients with poor MPR had a modestly elevated but non-significant risk (HR: 0.96; 95% CI: 0.67 to 1.36). Subgroup analysis revealed significantly elevated complication risk in patients ≥80 years with low COC (HR: 2.00; 95% CI: 1.67 to 2.32; p=0.04). The lowest complication rates were observed in patients receiving care from clinics with high COC and excellent MPR.Conclusions Higher levels of COC and MPR were associated with reduced angina-related complications, underscoring their importance in chronic disease management. However, the inconsistent statistical significance suggests disease-specific strategies may be needed to optimise continuity and adherence interventions. These findings have implications for refining ambulatory care models and enhancing chronic disease policies within Korea’s single-payer system.