ICD-10 Code K35.80 – Unspecified acute appendicitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code K35.80 – Unspecified acute appendicitis
What it is
K35.80 identifies acute appendicitis when the record confirms appendicitis but does not specify perforation, abscess, or generalized peritonitis. Use it for an acute inflammation of the appendix with limited detail in documentation.
Clinical signs
Typical findings include right lower quadrant abdominal pain, tenderness, nausea, vomiting, and fever. Clinical features vary; refer to documentation, especially when imaging or surgical notes do not describe complications.
When to use this code
Use this code when the provider documents acute appendicitis but does not identify a more specific type. It also fits cases where the chart lacks enough detail to assign a perforated or abscessed form. If documentation later clarifies complications, you should code the more specific diagnosis.
Do not use for
Do not use K35.80 for chronic appendicitis, appendicitis with perforation, or appendicitis with abscess. Check documentation if the record specifies generalized peritonitis or another complication.
Coding tip
Review operative, pathology, and imaging reports for complication details before defaulting to unspecified acute appendicitis.