K55.31
Stage 1 necrotizing enterocolitis
K55.31 (also written K5531) is a billable ICD-10-CM diagnosis code for stage 1 necrotizing enterocolitis. It is part of the FY2027 code set, effective October 1, 2026. It is one of the 27 codes in category K55 (Vascular disorders of intestine). The Alphabetic Index lists it under 2 entries. Its coding notes include 2 Excludes1 entries and 10 Excludes2 entries.
Excludes1
Not coded here. The listed conditions generally should not be reported together.
Excludes2
Not included here. Both codes may be reported if the patient has both conditions.
- necrotizing enterocolitis due to Clostridium difficile (A04.7-)
Also from chapter/block level (8 notes)
- 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)
Care settings
How CMS programs treat this code. These are CMS claim edits and list entries, not coverage or eligibility rules.
Home Health Primary
Accepted as the primary (principal) diagnosis on a home health claim. The Home Health Grouper assigns it to the MMTA - Other clinical group.
Source: CMS Home Health Grouper Software v07.2.26, effective October 1, 2026Hospital MCC
Counts as a major complication or comorbidity (MCC) when reported as a secondary diagnosis on an inpatient claim. It does not count when the principal diagnosis is one of the 23 codes in its exclusion list. Some MS-DRGs also ignore a CC or MCC that defines the DRG.
Source: CMS MS-DRG Definitions Manual v44, effective October 1, 2026, Appendix CInclusion terms
Conditions classified to this code.
- Necrotizing enterocolitis without pneumatosis, without perforation
Alphabetic Index terms
Terms the official Alphabetic Index lists for this code. 2 entries