Appendicitis ICD-10-CM codes

K35.80 (unspecified acute appendicitis) is the default for acute appendicitis without complications. K35.890 is other acute appendicitis without perforation or gangrene and K35.891 is other acute appendicitis with gangrene but without perforation. Appendicitis not specified as acute is K37, and chronic or recurrent appendicitis is K36.

Acute appendicitis with localized peritonitis is K35.3-: K35.30 without perforation or gangrene, K35.31 with gangrene, K35.32 with perforation and gangrene but no abscess, and K35.33 with perforation, gangrene, and abscess. Perforated appendicitis documented without further detail indexes to K35.32.

Acute appendicitis with generalized peritonitis is K35.2-, expanded to six characters in FY2023. Without abscess the codes are K35.200 (no perforation), K35.201 (with perforation), and K35.209 (perforation not specified); with abscess they are K35.210 (no perforation), K35.211 (with perforation), and K35.219 (perforation not specified). Because peritonitis is part of these codes, K65.0 is not reported separately for the appendiceal peritonitis.

Code the appendicitis based on the provider's diagnostic statement, not the pathology report alone; if pathology shows perforation or gangrene the provider did not document, query before assigning the higher-severity code.