Comparison of Nationwide Volumes for Five Major Gastrointestinal Surgical Procedures in Japan: Implications From Publicly Available NCD and NDB Open Data

ABSTRACT Aim In Japan, the National Clinical Database (NCD), a clinician‐reported registry, and the National Database of Health Insurance Claims and Specific Health Checkups of Japan Open Data (NDB Open Data), an administrative claims database, are both widely used as nationwide surgical databases, but their consistency in capturing national surgical volumes has not been systematically evaluated. Methods We compared publicly available data from the NCD annual surgical statistics and the NDB Open Data from 2014 to 2023. Annual case numbers were extracted for five major gastrointestinal procedures: cholecystectomy, inguinal hernia repair, appendectomy, colorectal cancer surgery, and gastric cancer surgery. Consistency was evaluated using three metrics: the median NCD/NDB ratio with interquartile range, Pearson's correlation coefficient for absolute annual volumes, and the proportion of years with concordant year‐to‐year change. Results The NCD generally reported higher case volumes than the NDB Open Data, with ratios ranging from close to unity (1.00) for colorectal cancer surgery to 1.10 for appendectomy. Temporal associations between the two databases (Pearson's r ) ranged from 0.70 to 0.99 across the five procedures. The proportion of years with concordant year‐to‐year change ranged from 44% for appendectomy to 100% for colorectal and gastric cancer surgery. Conclusion Despite relying on clinician‐reported data, the NCD demonstrated comparable temporal patterns to the NDB Open Data across the five major gastrointestinal procedures. The stability of procedure‐specific NCD/NDB ratios and the concordance of temporal trends support the use of NCD annual statistics for monitoring broad temporal trends in these selected gastrointestinal procedures in Japan.