K59.31
BillableToxic megacolon
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is K59.31 an HCC code?
Yes. K59.31 maps to Intestinal Obstruction/Perforation under the CMS-HCC V28 risk adjustment model (and Intestinal Obstruction/Perforation under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for K59.31
For K59.31to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed K59.31 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
K59.31 is the ICD-10-CM diagnosis code for toxic megacolon. A life-threatening condition where the colon becomes severely dilated and loses its ability to contract, often triggered by infection, medication, or electrolyte imbalances. K59.31 sits in the ICD-10-CM chapter for diseases of the digestive system (k00-k95), within the section covering other diseases of intestines (k55-k64).
Under the CMS-HCC V28 risk adjustment model, K59.31 maps to Intestinal Obstruction/Perforation (HCC 78) with a community, non-dual, aged base RAF weight of 0.326. Under the older V24 model, K59.31 mapped to the same category but with a base RAF weight of 0.219 — V28 recalibrated weights across the entire model. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
This is a serious condition requiring immediate documentation of the underlying trigger (C. difficile infection, medications, etc.). Because K59.31 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for K59.31 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a serious condition requiring immediate documentation of the underlying trigger (C. difficile infection, medications, etc.)
- •Code any associated complications separately (perforation, sepsis)
Clinical Significance
K59.31 represents toxic megacolon, a life-threatening complication where the colon becomes severely dilated and loses contractile function, often triggered by inflammatory bowel disease, infections, or medications. This condition requires immediate intensive care management and often surgical intervention to prevent perforation and sepsis.
Documentation Requirements
- ✓Radiographic evidence of severe colonic dilatation (>6cm)
- ✓Clinical signs of systemic toxicity (fever, tachycardia, altered mental status)
- ✓Documentation of underlying precipitating condition
- ✓Evidence of loss of colonic muscular tone
- ✓Intensive care monitoring and management
- ✓Assessment for perforation risk and surgical consultation
- ✓Documentation of medical vs surgical management approach
- ✓Monitoring for complications including perforation and sepsis
Commonly Confused Codes
- •K63.1 — Perforation of intestine (when perforation has actually occurred)
- •K56.7 — Ileus unspecified (when not specifically toxic megacolon)
- •K51.014 — Ulcerative colitis with toxic megacolon (when associated with UC)
- •A04.7 — Enterocolitis due to Clostridium difficile (when C. diff is precipitating cause)
- •R14.0 — Abdominal distention (symptom rather than specific toxic condition)