Reporting of Cohort and Routinely Collected Data in Randomised Controlled Trial Protocols (SPIRIT-ROUTINE): extension checklist with explanation and elaboration.

Randomised controlled trials that use cohorts or health-and-care systems data, often known as routinely collected data—such as electronic health records, registries, or administrative claims—are becoming increasingly common. These trials have the potential to streamline recruitment, intervention delivery, follow-up (within trial and long term), and to lower costs. The lack of clear information governance pathways, heterogeneous data quality, delays in data recording and acquisition, and regulatory or ethical complexities undermine reproducibility and bias assessment when routinely collected data are used in trials. We introduce the SPIRIT-ROUTINE extension to the SPIRIT 2025 guideline: a checklist and explanation designed to improve the reporting of trial protocols that rely on cohorts or routinely collected data sources. Investigators, funders, ethics committees, journal editors, and peer reviewers can use the SPIRIT-ROUTINE extension to enhance completeness, transparency, and usability of such protocols to support better research, healthcare decisions, and patient outcomes.