ICD-10 Code K35.21 – Acute appendicitis with generalized peritonitis, with abscess (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code K35.21 – Acute appendicitis with generalized peritonitis, with abscess
What it is
This code identifies acute inflammation of the appendix with generalized peritonitis and a documented abscess. Use it when the record shows appendicitis has spread beyond the appendix and caused diffuse peritoneal infection.
Clinical signs
Clinical features commonly include abdominal pain, guarding, rebound tenderness, and signs of peritoneal irritation. Imaging or operative findings may show an abscess; if details differ, check documentation.
When to use this code
Use K35.21 when the provider documents acute appendicitis with generalized peritonitis and an abscess. It also fits when surgery, imaging, or discharge summary confirms both diffuse peritoneal involvement and abscess formation.
If the record only says appendicitis with localized peritonitis, perforation, or abscess without generalized peritonitis, this code may not apply. Verify the exact wording before assigning the diagnosis.
Do not use for
Do not use this code for uncomplicated appendicitis, localized peritonitis only, or appendiceal abscess without generalized peritonitis. Check documentation if the extent of peritoneal involvement is unclear.
Coding tip
Code from the most specific provider statement, and confirm that both generalized peritonitis and abscess are documented.