What works to reduce socioeconomic inequalities in hospitalisations and readmissions? Systematic review of the equity impacts of population-level, health service and integrative interventions.

Inequalities exist in hospitalisation rates, which are undesirable and costly for health systems; with higher rates in populations with lower levels of income, education or residing in socioeconomically marginalised neighbourhoods where ill-health is more prevalent and preventive care is more limited. Objectives: To understand which interventions reduce, maintain or increase socioeconomic inequalities in hospitalisations or readmissions to aid efforts of policymakers and practitioners working to improve health equity and reduce hospital pressures. Design: Systematic review. Eligibility criteria: Intervention studies in any Organisation for Economic Co-operation and Development (OECD) country, involving individuals of any age, published in any language which reported the differential impact across socioeconomic group (any classification) for three categories of intervention (population-level, health service or integrative interventions) on hospitalisation or readmission outcomes (all cause or condition specific). Data extraction and synthesis: An electronic search of MEDLINE, Embase, CINAHL, Cochrane CENTRAL and Web of Knowledge was conducted covering 24 years (from 1 January 2000 to 1 April 2024), supplemented with full citation searches of included studies, website searches and expert consultation. Risk of bias was assessed using the EHPP tool, direction of effect classified and narrative synthesis conducted. Results: From 25 618 records screened, 36 studies met the inclusion criteria, conducted in eight countries with 42% of these published in the past 5 years. Studies employed a range of study designs and 88% were rated as either moderate or strong quality. A range of equity impacts of interventions on hospitalisations and readmissions were observed; 6 interventions increased inequalities, 7 maintained, 10 had mixed or inconclusive impacts, and 13 studies reported effective interventions for reducing inequalities. Interventions successful at reducing inequalities were those implemented and enforced across entire populations and systems and supportive interventions tailored to the varied needs and contexts of people from different socioeconomic groups. Conclusions: Socioeconomic disadvantage was variously measured making comparison of equity impacts across studies complex. Policymakers and practitioners cannot assume that interventions implemented to reduce hospitalisations or readmissions will necessarily reduce prevailing and costly healthcare inequalities; it is imperative that the equity impacts of interventions are consistently monitored. To improve equity of hospital outcomes, investment in population health and integrative activity addressing the social determinants of health, alongside health service interventions, is required. PROSPERO registration number: CRD42019153666.