Evaluating professional interpreting services for patients with limited English proficiency in secondary care settings: a scoping review.

BACKGROUND: Patients with limited English proficiency (LEP) face significant language barriers in healthcare, leading to poorer clinical outcomes. Professional medical interpreters are essential for equitable, high-quality care. While their use is widely recommended, there is limited understanding of the optimal objective outcome measures to best evaluate interpreter effectiveness in secondary and tertiary care settings. METHODS: A scoping review was conducted which was prospectively registered on the Open Science Framework and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) guidelines. Four databases (MEDLINE, PubMed, Embase and CINAHL) were searched without date or language limits. We included comparative studies assessing professional medical interpreting services for adult patients with LEP in secondary or tertiary care using objective outcome measures related to clinical outcomes and/or healthcare utilisation. Data extraction included study design, interpreter modalities, outcome measures and adjustments for confounders. RESULTS: Eleven studies met the inclusion criteria. Most were cohort or cross-sectional studies, predominantly conducted in the USA. The most common outcome measures were clinical, including length of stay (n=8), readmission (n=5) and return emergency visits (n=3). Four studies assessed healthcare utilisation, including outpatient appointment adherence. Results varied: some studies showed reduced length of stay and readmissions with interpreter use, while others found longer stays or no effect. Disease-specific outcomes (e.g., stroke care quality and obstetric indicators) consistently favoured interpreter or health advocate use. Adjustment for confounders was inconsistent with few studies accounting for illness severity. CONCLUSION: This review highlights the heterogeneity and limitations in existing outcome measures for evaluating interpreter services. Length of stay and readmission are commonly used but prone to confounding. Disease-specific outcomes may offer greater sensitivity and relevance, especially when adjusted for clinical severity. Future research should prioritise the development of validated, standardised outcome sets that reflect both patient priorities and clinical relevance. These are essential for guiding service improvement and equitable healthcare delivery for LEP populations.