K55.31
BillableStage 1 necrotizing enterocolitis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is K55.31 an HCC code?
Yes. K55.31 maps to Vascular Disease with Complications under the V24 model but is not retained in V28.
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 K55.31
For K55.31to 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 K55.31 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
K55.31 is the ICD-10-CM diagnosis code for stage 1 necrotizing enterocolitis. The earliest stage of necrotizing enterocolitis in newborns, characterized by initial signs of intestinal inflammation without significant tissue death. K55.31 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 older CMS-HCC V24 model, K55.31 maps to Vascular Disease with Complications (HCC 107) with a community, non-dual, aged base RAF weight of 0.450. 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.
Stage 1 is the mildest form; progression to higher stages should be documented with new codes. Because K55.31 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 K55.31 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Stage 1 is the mildest form; progression to higher stages should be documented with new codes
- •Include clinical presentation details such as feeding intolerance and abdominal distension
Clinical Significance
Stage 1 necrotizing enterocolitis represents early neonatal intestinal inflammation requiring intensive monitoring and potential progression to more severe stages. This condition indicates high-risk neonatal pathology requiring specialized NICU care and careful surveillance for complications.
Documentation Requirements
- ✓Neonatal patient with feeding intolerance
- ✓Clinical criteria for Stage 1 NEC documented
- ✓Mild systemic signs and symptoms
- ✓Imaging showing intestinal distention or pneumatosis
- ✓Treatment interventions implemented
- ✓Monitoring for disease progression
- ✓NICU level care provided