2027 ICD-10-CM Diagnosis Code K55.31Stage 1 necrotizing enterocolitis
ICD-10-CM Codes›K00–K95›K55-K64›K55
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- Not Chronic
K55.31 is a billable ICD-10-CM diagnosis code for stage 1 necrotizing enterocolitis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 393 through 395, 791, 793. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 23 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified and unspecified gastrointestinal disorders.
K55.31 no longer risk-adjusts for Medicare Advantage: it mapped to HCC 107 under the retired CMS-HCC V24 model through payment year 2025 but maps to no category in the live V28 model. It still risk-adjusts in the PACE (CMS-HCC V22) category 107, ESRD (V21) category 107, and ESRD (V24) category 107 for payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
K55.31 no longer risk-adjusts for Medicare Advantage: it maps to no payment category in the live CMS-HCC V28 model, although it still risk-adjusts in the other CMS models shown below.
Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to K55.31: its own notes plus those printed at K55.3, K55, and Chapter 11. A note printed at a category, block or chapter applies to every code under it.
Applicable To
Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.
- Necrotizing enterocolitis without pneumatosis, without perforation
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
- necrotizing enterocolitis due to Clostridium difficile (A04.7-)
- angioectasia (angiodysplasia) duodenum (K31.81-)
- certain conditions originating in the perinatal period (P04-P96)
- certain infectious and parasitic diseases (A00-B99)
- complications of pregnancy, childbirth and the puerperium (O00-O9A)
- congenital malformations, deformations and chromosomal abnormalities (Q00-Q99)
- endocrine, nutritional and metabolic diseases (E00-E88)
- injury, poisoning and certain other consequences of external causes (S00-T88)
- neoplasms (C00-D49)
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Enterocolitis See Also: Enteritis; K52.9
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Enterocolitis, Necrotizing
enterocolitis with extensive ulceration (ulcer) and necrosis. it is observed primarily in low birth weight infant.
Patient EducationClinical
Digestive Diseases
When you eat, your body breaks food down to a form it can use to build and nourish cells and provide energy. This process is called digestion.
Read the full article at MedlinePlus
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Convert K55.31 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code History & ChangesHistory
Replacement K55.31 replaces the following previously assigned code(s):
- K55.8 - Other vascular disorders of intestine
Questions About K55.31Overview
What is the ICD-10 code for stage 1 necrotizing enterocolitis?
The ICD-10-CM code for stage 1 necrotizing enterocolitis is K55.31 (sometimes written as K5531). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is K55.31 (Necrotizing enterocolitis) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report stage 1 necrotizing enterocolitis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does K55.31 group to?
When stage 1 necrotizing enterocolitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 791, 394, 395, 393, with relative weights from 0.6379 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.
Is K55.31 a CC or MCC?
CMS lists K55.31 as an MCC (major complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 23 closely related codes in its exclusion list.
Can K55.31 be reported with a code from P77?
Not as a rule. The Excludes1 note at K55.3, which applies to K55.31, lists "necrotizing enterocolitis of newborn (P77.-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
Does K55.31 risk-adjust for Medicare Advantage payment?
Not for Medicare Advantage. K55.31 mapped to HCC 107 in the retired CMS-HCC V24 model, which last determined payment in 2025, but it maps to no category in the live V28 model; see all codes that no longer risk-adjust. It still risk-adjusts in the PACE (CMS-HCC V22) category 107 (Vascular Disease with Complications), ESRD (V21) category 107 (Vascular Disease with Complications), and ESRD (V24) category 107 (Vascular Disease with Complications).
