Table 1.

Definition of episode of care and reference case

Definition
Name	Appendectomy
Defined by	Primary diagnosis and procedure
Primary diagnosis (ICD-10-WHO V2007)a	K35: Acute appendicitis
	K36: Other appendicitis
	K37: Unspecified appendicitis
	K38: Other diseases of appendix
Procedure (ICD-9CM V2008)	47.0: Appendectomy, including
	47.01: Laparoscopic appendectomy
	47.09: Other appendectomy
Index case
Adult age (<70), uncomplicated appendicitis without complications, open appendectomy, treated as inpatient

^aA full list of relevant ICD-10 codes is provided as Electronic supplementary material