ICD-10 Code K35.209 – Acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code K35.209 – Acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation
What it is
This code identifies acute appendicitis complicated by generalized peritonitis, but without an abscess. Use it when the record does not specify whether the appendix is perforated.
Clinical signs
Typical findings include acute abdominal pain with diffuse peritoneal irritation, guarding, and rebound tenderness. Clinical features vary; refer to documentation for evidence of generalized peritonitis and any mention of abscess or perforation.
When to use this code
Use K35.209 when the provider documents acute appendicitis with generalized peritonitis and no abscess, and perforation status is not stated. It also fits when imaging, operative notes, or discharge summaries support diffuse peritoneal involvement. If the record later specifies perforation, code the documented condition instead.
Do not use for
Do not use this code for appendicitis with a localized abscess, or when generalized peritonitis is not documented. Check documentation if the note specifies perforation, because a different code may apply.
Coding tip
Verify the operative report and final diagnosis for abscess and perforation details before assigning K35.209.