ICD-10 Code K35 – Acute appendicitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code K35 – Acute appendicitis
What it is
K35 identifies acute appendicitis, an abrupt inflammation of the appendix. Use it when the record documents a new, active appendiceal infection or inflammation requiring diagnosis coding.
Clinical signs
Typical findings include abdominal pain, often starting near the umbilicus and moving to the right lower quadrant, with tenderness and guarding. Clinical features vary; refer to documentation.
When to use this code
Use K35 when the provider documents acute appendicitis, whether the note is based on exam, imaging, surgery, or pathology. It applies to confirmed acute cases and should match the documented subtype if one is specified. If the chart does not clearly state acute appendicitis, check documentation.
Do not use for
Do not use K35 for chronic appendiceal disease, history of appendectomy, or abdominal pain without a confirmed diagnosis. Check documentation for the correct condition.
Coding tip
Code the most specific documented appendicitis type and verify whether perforation, abscess, or generalized peritonitis is stated.