The International Classification of Diseases (ICD) is a globally recognized system for coding diseases, conditions, and health-related findings, maintained by the World Health Organization.
In clinical research, ICD codes support standardized identification of diagnoses and medical history elements used in eligibility, stratification, and endpoint characterization. Coding consistency improves comparability across sites, studies, and data sources, including claims and electronic records. Standardized classification strengthens data quality for analysis and reporting. ICD-based coding also supports interoperability and downstream regulatory or health economics analyses.