Clarity in Reporting Multiple Long-Term Conditions in Research: The Need for Consistency and Consensus.

Multiple long-term conditions (MLTC), also known as multimorbidity, affects a substantial proportion of the global population and represents an increasing challenge to healthcare systems, individuals and society. Despite increasing attention and investment, progress in MLTC research is hindered by conceptual inconsistencies and a lack of standardised reporting. Challenges include varied terminology, differing definitions of chronicity and substantial variation in the number and type of conditions included across studies. These inconsistencies contribute to differences in prevalence estimates and reduced comparability across the literature. Moreover, many clinical trials involve participants living with MLTC but do not collect or report co-existing conditions, leaving their experiences largely invisible within research and limiting applicability of findings for this population. Heterogeneity in disease clusters and outcome selection further complicates evidence synthesis. In this commentary, we highlight that improving the clarity and impact of MLTC research requires transparent reporting of MLTC status, the use of consensus-based condition lists, identification of clinically and socially meaningful clusters and prioritisation of outcomes aligned with what matters most to people living with MLTC (e.g., independence, treatment burden and quality of life). Improving reporting practices is needed to generate evidence that improves care, informs policy and enhances the wellbeing of people living with MLTC.