ICD-10 Code K35.3 – Acute appendicitis with localized peritonitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code K35.3 – Acute appendicitis with localized peritonitis
What it is
K35.3 identifies acute appendicitis with inflammation limited to the area around the appendix. It is used when the appendix is inflamed and nearby peritoneal irritation is documented.
Clinical signs
Typical findings include abdominal pain, guarding, and localized tenderness, often in the right lower quadrant. Clinical features vary; refer to documentation for confirmation of localized peritonitis.
When to use this code
Use K35.3 when the record clearly states acute appendicitis with localized peritonitis or equivalent wording such as localized peritoneal irritation. You should code it when the provider documents appendicitis plus inflammation confined to the local area. Check documentation if the note only says appendicitis without peritoneal involvement.
Do not use for
Do not use this code for appendicitis without peritonitis, generalized peritonitis, or a ruptured appendix unless the documentation supports K35.3. If the record is unclear, check documentation.
Coding tip
Assign K35.3 only when localized peritonitis is explicitly documented, not inferred from pain alone.