ICD-10 Code K51.313 – Ulcerative (chronic) rectosigmoiditis with fistula (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code K51.313 – Ulcerative (chronic) rectosigmoiditis with fistula
What it is
This code identifies chronic ulcerative colitis limited to the rectosigmoid area, with a fistula present. Use it when documentation shows both the rectosigmoid involvement and the abnormal tract.
Clinical signs
Typical findings include chronic inflammatory bowel symptoms involving the rectum and sigmoid colon, with evidence of a fistula. Clinical features vary; refer to documentation for the exact site and type of fistula.
When to use this code
Use K51.313 when the provider documents ulcerative rectosigmoiditis and also states a fistula related to the disease. The record should support chronic ulcerative colitis in the rectosigmoid region, not a different colitis subtype.
If the fistula is mentioned without clear rectosigmoid involvement, or if the diagnosis is not confirmed as chronic ulcerative disease, check documentation before coding. Code the documented condition as written.
Do not use for
Do not use this code for Crohn’s disease, nonspecific colitis, or ulcerative colitis without fistula. Do not assume a fistula site or bowel segment if the note does not specify it.
Coding tip
Confirm both elements in the note: rectosigmoid ulcerative colitis and fistula; if either is unclear, query the provider.