ICD-10 Code K35.89 – Other acute appendicitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code K35.89 – Other acute appendicitis
What it is
K35.89 identifies an acute appendicitis diagnosis that does not fit a more specific appendicitis code. Use it when the record clearly supports acute appendiceal inflammation, but the subtype is not otherwise documented.
Clinical signs
Typical findings include right lower quadrant abdominal pain, tenderness, and signs of acute inflammation. Clinical features vary; refer to documentation for the exact presentation and any imaging or operative confirmation.
When to use this code
Use K35.89 when the provider documents acute appendicitis and does not specify perforation, gangrene, generalized peritonitis, or another more precise type. It also fits cases where the note states “other” or leaves the subtype unspecified.
Check documentation if the chart suggests a different acute appendicitis category, because a more specific code may apply. Do not assume this code for chronic, recurrent, or postoperative abdominal pain without acute appendiceal inflammation.
Do not use for
Do not use K35.89 for chronic or recurrent appendicitis, or when the record documents perforation, abscess, or generalized peritonitis. If the diagnosis is unclear, check documentation.
Coding tip
Code the most specific appendicitis type documented; if the subtype is missing, K35.89 is the fallback.