2026 ICD-10-CM Diagnosis Code P77.9Necrotizing enterocolitis in newborn, unspecified

ICD-10-CM Codes›P00–P96›P76-P78›P77

ICD-10-CM P77.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

P77.9 is a billable ICD-10-CM diagnosis code for necrotizing enterocolitis in newborn, unspecified. 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 acute radiation enteritis of intestine. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Neonatal digestive and feeding disorders.

For Medicare Advantage risk adjustment, P77.9 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

ICD-10-CM Code
P77.9
Billable Status
Yes — Valid for Submission
Code Describes
Necrotizing enterocolitis in newborn, unspecified
Short Description
Necrotizing enterocolitis in newborn, unspecified
Same as the full description in the CMS dataset.
Parent Code
P77
Necrotizing enterocolitis of newborn

Code Classification

ChapterP00–P96Certain conditions originating in the perinatal period
SectionP76-P78Digestive system disorders of newborn
CategoryP77Necrotizing enterocolitis of newborn
This CodeP77.9Necrotizing enterocolitis in newborn, unspecified

Medicare Risk Adjustment (HCC)Billing

P77.9 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.

CMS-HCC V28 Category (Payment Model)
HCC 78— Intestinal Obstruction/Perforation
Payment HCC · PY 2026 one of 76 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.326
community, non-dual, aged · ranges 0.326–0.688 across segments
Hierarchy
Superseded by HCC 77
a more severe related category takes the payment when both are reported
Prior Model (CMS-HCC V24)
Not mapped under V24
this diagnosis newly risk-adjusts under the V28 model
Part D (RxHCC)
Not mapped
P77.9 does not risk-adjust in the RxHCC prescription drug model

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.

  • Acute radiation enteritis of intestine
  • Colitis
  • Fetal and/or neonatal necrotizing enterocolitis
  • Gastroenteritis
  • Neonatal necrotizing enterocolitis
  • Noninfectious enteritis of intestine
  • Noninfectious gastroenteritis
  • Noninfective enteritis and colitis
  • Perinatal necrotizing enterocolitis
  • Radiation enteritis of intestine

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Necrotizing enterocolitis in newborn, NOS

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR PNL012
Neonatal digestive and feeding disorders
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Gastroenteritis

    inflammation of any segment of the gastrointestinal tract from esophagus to rectum. causes of gastroenteritis are many including genetic, infection, hypersensitivity, drug effects, and cancer.

  • Gastroenteritis, Transmissible, of Swine

    a condition of chronic gastroenteritis in adult pigs and fatal gastroenteritis in piglets caused by a coronavirus.

  • Murine hepatitis virus

    a species of the coronavirus genus causing hepatitis in mice. four strains have been identified as mhv 1, mhv 2, mhv 3, and mhv 4 (also known as mhv-jhm, which is neurotropic and causes disseminated encephalomyelitis with demyelination as well as focal liver necrosis).

  • Transmissible gastroenteritis virus

    a species of coronavirus causing a fatal disease to pigs under 3 weeks old.

  • Colitis

    inflammation of the colon section of the large intestine (intestine, large), usually with symptoms such as diarrhea (often with blood and mucus), abdominal pain, and fever.

  • Colitis, Collagenous

    a subtype of microscopic colitis, characterized by chronic watery diarrhea of unknown origin, a normal colonoscopy but abnormal histopathology on biopsy. microscopic examination of biopsy samples taken from the colon show larger-than-normal band of subepithelial collagen.

  • Colitis, Ischemic

    inflammation of the colon due to colonic ischemia resulting from alterations in systemic circulation or local vasculature.

  • Colitis, Lymphocytic

    a subtype of microscopic colitis, characterized by chronic watery diarrhea of unknown origin, a normal colonoscopy but abnormal histopathology on biopsy. microscopic examination of biopsy samples taken from the colon show infiltration of lymphocytes in the superficial epithelium and the underlying connective tissue (lamina propria).

  • Colitis, Microscopic

    a condition characterized by chronic watery diarrhea of unknown origin, a normal colonoscopy but abnormal histopathology on biopsy. this syndrome was first described in 1980 by read and associates. subtypes include collagenous colitis and lymphocytic colitis. both have similar clinical symptoms and are distinguishable only by histology.

  • Colitis, Ulcerative

    inflammation of the colon that is predominantly confined to the mucosa. its major symptoms include diarrhea, rectal bleeding, the passage of mucus, and abdominal pain.

  • Colitis-Associated Neoplasms

    colonic neoplasms associated with chronic inflammation conditions such as ulcerative colitis and crohn disease.

  • Crohn Disease

    a chronic transmural inflammation that may involve any part of the digestive tract from mouth to anus, mostly found in the ileum, the cecum, and the colon. in crohn disease, the inflammation, extending through the intestinal wall from the mucosa to the serosa, is characteristically asymmetric and segmental. epithelioid granulomas may be seen in some patients.

  • Cytomegalovirus Infections

    infection with cytomegalovirus, characterized by enlarged cells bearing intranuclear inclusions. infection may be in almost any organ, but the salivary glands are the most common site in children, as are the lungs in adults.

  • Dysentery, Amebic

    dysentery caused by intestinal amebic infection, chiefly with entamoeba histolytica. this condition may be associated with amebic infection of the liver and other distant sites.

  • Enterocolitis, Pseudomembranous

    an acute inflammation of the intestinal mucosa that is characterized by the presence of pseudomembranes or plaques in the small intestine (pseudomembranous enteritis) and the large intestine (pseudomembranous colitis). it is commonly associated with antibiotic therapy and clostridium difficile colonization.

  • Irritable Bowel Syndrome

    a disorder with chronic or recurrent colonic symptoms without a clearcut etiology. this condition is characterized by chronic or recurrent abdominal pain, bloating, mucus in feces, and an erratic disturbance of defecation.

  • Coronavirus

    a member of coronaviridae which causes respiratory or gastrointestinal disease in a variety of vertebrates.

  • Cytomegalovirus

    a genus of the family herpesviridae, subfamily betaherpesvirinae, infecting the salivary glands, liver, spleen, lungs, eyes, and other organs, in which they produce characteristically enlarged cells with intranuclear inclusions. infection with cytomegalovirus is also seen as an opportunistic infection in aids.

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 P77.9 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
777.50 Nec enterocoltis NB NOS
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About P77.9Overview

What is the ICD-10 code for necrotizing enterocolitis in newborn, unspecified?

The ICD-10-CM code for necrotizing enterocolitis in newborn, unspecified is P77.9 (sometimes written as P779). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Is P77.9 (Necrotizing enterocolitis of newborn) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report necrotizing enterocolitis in newborn, unspecified on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does P77.9 group to?

When necrotizing enterocolitis in newborn, unspecified 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 P77.9 a CC or MCC?

CMS lists P77.9 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 P77.9?

Under the General Equivalence Mappings, necrotizing enterocolitis in newborn, unspecified converts to ICD-9-CM 777.50 (nec enterocoltis NB NOS). The mapping is a direct match.

What HCC is P77.9?

P77.9 (necrotizing enterocolitis in newborn, unspecified) 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 P77.9 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, P77.9 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.