Heatwaves are among the fastest-growing climate-related threats to human health, increasing in frequency, intensity and duration with climate change. Older adults are disproportionately affected, reflecting intersecting physiological, social and economic vulnerabilities. Beyond mortality, heatwaves drive substantial but often under-recognised morbidity, including emergency visits and hospitalisations for cardiovascular, respiratory, renal and metabolic conditions. Health administrative data provide valuable opportunities to improve understanding of these phenomena and for the quantification of their impacts. However, comparability is limited by heterogeneity in case definitions, that is, the criteria used to determine which health events are counted as cases: some studies only clinically diagnosed heat illness, while others also capture outcomes plausibly triggered or exacerbated by heat. It is further constrained by differences in International Classification of Diseases (ICD) versions, national adaptations, coding practices and adoption timelines across countries. No synthesis has yet mapped these heterogeneous approaches for older adults, despite their over-representation among those most affected by heat-health risks. This heterogeneity limits the ability to capture the true burden of disease and to inform adaptation planning.

We will conduct a scoping review to map how heat-related diagnoses among older adults are identified and measured in health administrative data. The review will follow the initial methodological framework of Arksey and O’Malley refined by Levac et al and adhere to the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews) guidelines. The search strategy will be developed with a public health librarian and applied to MEDLINE (Ovid), Embase and Web of Science. We will include peer-reviewed and grey literature published in English or French from 2010 onward. Two reviewers will independently screen titles, abstracts and full texts in Covidence, with disagreements resolved by consensus or a third reviewer. Data will be extracted using a standardised form to capture study characteristics, ICD codes, definitions of heat exposure and approaches to measurement. A descriptive and thematic analysis will be conducted, and findings will be presented narratively and in tables.

Ethical approval is not required for this review as it involves secondary analysis of published and publicly available data; for more information, contact University of Montreal’s Research Integrity department at plaintes-crr@umontreal.ca. Results will be published through a peer-reviewed publication, conference presentations and knowledge transfer activities with public health stakeholders in Québec. This review contributes to the MEDICCS (Modélisation économique des impacts des changements climatiques sur la santé) project and will support recommendations for improving the capture of heat-related morbidity in health administrative data.