2026 ICD-10-CM Diagnosis Code P77.1Stage 1 necrotizing enterocolitis in newborn
ICD-10-CM Codes›P00–P96›P76-P78›P77
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- Risk Adjusts — HCC 78
- Not Chronic
P77.1 is a billable ICD-10-CM diagnosis code for stage 1 necrotizing enterocolitis in newborn. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 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 36 closely related codes. Coders also document this condition as fetal and/or neonatal necrotizing enterocolitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Neonatal digestive and feeding disorders.
For Medicare Advantage risk adjustment, P77.1 maps to CMS-HCC Category 78 (Intestinal Obstruction/Perforation) under the V28 model, adding a risk factor of about 0.326 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
P77.1 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 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.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Fetal and/or neonatal necrotizing enterocolitis
- Necrotizing enterocolitis of newborn, stage 1A
- Necrotizing enterocolitis of newborn, stage 1B
- Neonatal necrotizing enterocolitis
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Necrotizing enterocolitis without pneumatosis, without perforation
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
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.
Patient EducationClinical
Premature Babies
Almost 1 of every 10 infants born in the United States are premature, or preemies. A premature birth is when a baby is born before 37 completed weeks of pregnancy. A full-term pregnancy is 40 weeks.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert P77.1 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About P77.1Overview
What is the ICD-10 code for stage 1 necrotizing enterocolitis in newborn?
The ICD-10-CM code for stage 1 necrotizing enterocolitis in newborn is P77.1 (sometimes written as P771). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is P77.1 (Necrotizing enterocolitis of newborn) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report stage 1 necrotizing enterocolitis in newborn on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does P77.1 group to?
When stage 1 necrotizing enterocolitis in newborn is the principal diagnosis on an inpatient stay, it groups to MS-DRG 791, 793, with relative weights from 4.0590 to 4.1696 depending on complications. Higher weights mean higher Medicare reimbursement.
Is P77.1 a CC or MCC?
CMS lists P77.1 as an MCC (major complication or comorbidity) for FY 2026. 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 36 closely related codes in its exclusion list.
What is the ICD-9 equivalent of P77.1?
Under the General Equivalence Mappings, stage 1 necrotizing enterocolitis in newborn converts to ICD-9-CM 777.51 (stg I nec enterocol NB). The mapping is a direct match.
What HCC is P77.1?
P77.1 (stage 1 necrotizing enterocolitis in newborn) maps to CMS-HCC Category 78 (Intestinal Obstruction/Perforation), commonly written as HCC 78, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It does not map to any RxHCC in the Part D prescription drug model.
Does P77.1 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, P77.1 adds a risk adjustment factor of about 0.326 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.326 to 0.688 depending on the payment segment). A more severe related category (HCC 77) supersedes it when both are reported. See the full factor table on the HCC 78 category page.
