Outcome measurement for multiple long-term conditions research across health-care settings – an overview of reviews

BACKGROUND: Multiple long-term conditions (MLTC) represent a growing global public health challenge, yet research is hindered by inconsistent outcomes across health-care settings and populations. Although several core outcome sets (COS) have been developed, important gaps remain in their coverage, inclusivity, and measurement validity. This overview of reviews summarised outcomes reported in systematic reviews of MLTC research to identify existing domains, describe how measurement instruments were addressed, and highlight areas requiring standardisation. METHODS: We conducted a prospectively registered overview of reviews (PROSPERO CRD420251005152), following PRISMA, PRIOR, and SWiM guidelines. Eligible reviews included adults or children with MLTC-defined as the coexistence of two or more chronic conditions-and reported on outcome measures or COS relevant to this population. Five databases (MEDLINE, CINAHL, Scopus, Cochrane Library, COMET (Core Outcome Measures in Effectiveness Trials)) were searched from inception to April 2025. Two reviewers independently screened, extracted data, and appraised quality using the Joanna Briggs Institute checklist. A narrative synthesis mapped outcomes by domain (clinical, patient-reported, service/system, engagement/experience), care setting, and population subgroup. RESULTS: From 6331 records, 10 reviews met inclusion criteria, encompassing 709 primary studies. Four developed COS, and six mapped outcomes without proposing COS. Quality of life and health-care utilisation were most consistently reported; treatment burden, patient engagement, and child outcomes were infrequently assessed. Existing COS advanced standardisation but remained limited in stakeholder diversity, geographic scope, and specification of measurement instruments, with only one including low- and middle-income countries. CONCLUSIONS: Greater inclusivity, validation, and global applicability are needed to operationalise agreed domains and improve comparability across MLTC research.