Date of Service (DOS) is the documented date on which a clinical trial-related visit, procedure, test, or service is performed.
DOS is used to track protocol-required activities, confirm visit scheduling compliance, and support accurate source documentation. It is also critical for billing workflows and coverage analysis when distinguishing routine care from research-billed services. Accurate DOS recording improves auditability across clinical, operational, and financial records. Consistent documentation supports transparency and compliance in research billing and recordkeeping.