K65.4 ICD-10-CM Code: Sclerosing mesenteritis

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for K65.4 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on K65.4 itself; “inherited from” names the category or block whose note applies here.

Coder workflow for K65.4

MedCoder structured workflow — derived from this code’s own official record

Before you code K65.4

1. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with K65.4. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

   See the official tabular notes

Choose the right path

1. Does the documentation support a condition named in K65.4’s Excludes1 note?
   Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
   No → Continue.

   ReviewK35.2, T81.6, E85.0, A54.85, A74.81, A36.89

Consider K65.4. Then work the Use Additional Code note and review the Code Also note, and confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement

Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).

The conditions the Use Additional Code note names

Reported with this code when documented; a conditional instruction (“if applicable”, “if known”) applies only when the record supports it.

Official instructions as workflow

• Excludes1 — check before selecting K65.4(17 notes)

  Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with K65.4: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

  CompareK35.2, T81.6, E85.0, A54.85, A74.81, A36.89

  See the official tabular notes · Guidelines I.A.12.a

• Use Additional Code — after identifying K65.4(1 note)

  Coding workflow: Check whether the documentation supports the additional code(s) the note names, and report them with K65.4 when it does. Where the instruction is conditional (“if applicable”, “if known”), it applies only when the record documents the condition.

  See the official tabular notes · Guidelines I.A.13

• Code Also — related condition(1 note)

  Coding workflow: Review the related condition when both are documented and the instruction applies. A Code Also note does not fix sequencing; the order follows the circumstances of the encounter.

  ReviewK57

  See the official tabular notes · Guidelines I.A.17

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Indexed Clinical Terms (14)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

• Fat, necrosis, mesentery
• Fat, necrosis, omentum
• Fibrosis, fibrotic, sclerosing mesenteric (idiopathic)
• Lipodystrophy, mesenteric
• Mesenteritis, retractile
• Mesenteritis, sclerosing
• Necrosis, necrotic (ischemic), fat, fatty (generalized), abdominal wall
• Necrosis, necrotic (ischemic), fat, fatty (generalized), mesentery
• Necrosis, necrotic (ischemic), fat, fatty (generalized), omentum
• Necrosis, necrotic (ischemic), fat, fatty (generalized), peritoneum
• Necrosis, necrotic (ischemic), mesentery, fat
• Necrosis, necrotic (ischemic), omentum (with mesenteric infarction), fat
• Necrosis, necrotic (ischemic), peritoneum (with mesenteric infarction), fat
• Panniculitis (nodular) (nonsuppurative), mesenteric

Official Coding Guidelines

No excerpt in the ICD-10-CM Official Guidelines names this code specifically. Its chapter carries only this chapter-wide note:

Don’t confuse K65.4 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of K65.4 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

• K35.2— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of acute appendicitis with generalized peritonitis moves the case to K35.2; the two are not reported together unless documented as unrelated.

  Full comparison: K65.4 vs K35.2 →

• T81.6— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of aseptic peritonitis moves the case to T81.6; the two are not reported together unless documented as unrelated.

  Full comparison: K65.4 vs T81.6 →

• E85.0— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of benign paroxysmal peritonitis moves the case to E85.0; the two are not reported together unless documented as unrelated.

  Full comparison: K65.4 vs E85.0 →

• A54.85— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of gonococcal peritonitis moves the case to A54.85; the two are not reported together unless documented as unrelated.

  Full comparison: K65.4 vs A54.85 →

• P78.0— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of neonatal peritonitis moves the case to P78.0; the two are not reported together unless documented as unrelated.

  Full comparison: K65.4 vs P78.0 →

• P78.1— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of neonatal peritonitis moves the case to P78.1; the two are not reported together unless documented as unrelated.

  Full comparison: K65.4 vs P78.1 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Decision Points

The directives on this code's own record, as a pre-claim checklist.

1. 1 Use Additional Code instruction — report the named additional code(s) when the documentation supports them. See the Use Additional Code notes
2. 1 Code Also note — a second code may apply; the guidelines leave its sequencing to the circumstances of the encounter. See the Code Also notes
3. 17 Excludes1 entries — codes named there are generally not reported together with this code (Guidelines I.A.12.a). See the Excludes1 notes

Checklist rows are derived from this code's own official directives; the wording of each check is MedCoder editorial. The official notes themselves are in the sections each row links to.

Verify Before Coding

• CC as a secondary diagnosis (FY2026). Can raise the stay's MS-DRG severity tier.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name K65.4 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 1 Code Also instruction: K57 — Diverticular disease of intestine (via K65.-).

These codes suggest coding this condition alongside when both are present.

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: CC — Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 22 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 5 MS-DRGs: DRG 393 (MDC 06), DRG 394 (MDC 06), DRG 395 (MDC 06), DRG 791 (MDC 15), DRG 793 (MDC 15).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):DIG016 — Peritonitis and intra-abdominal abscess (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical process (MS-DRG)

Acts as CC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

K63.8211 — Small intestinal bacterial overgrowth, hydrogen-subtype, K63.8212 — Small intestinal bacterial overgrowth, hydrogen sulfide-subtype, K63.8219 — Small intestinal bacterial overgrowth, unspecified, K63.822 — Small intestinal fungal overgrowth, K63.829 — Intestinal methanogen overgrowth, unspecified, K63.89 — Other specified diseases of intestine, K63.9 — Disease of intestine, unspecified, K65.0 — Generalized (acute) peritonitis, K65.1 — Peritoneal abscess, K65.2 — Spontaneous bacterial peritonitis, K65.3 — Choleperitonitis, K65.8 — Other peritonitis, K65.9 — Peritonitis, unspecified, K68.19 — Other retroperitoneal abscess, K68.2 — Retroperitoneal fibrosis, K68.3 — Retroperitoneal hematoma, K68.9 — Other disorders of retroperitoneum, K92.89 — Other specified diseases of the digestive system, K92.9 — Disease of digestive system, unspecified, R11.13 — Vomiting of fecal matter, +1 more

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Intestinal Obstruction/Perforation) for risk-adjusted payment.

K56.690 — Other partial intestinal obstruction, K56.691 — Other complete intestinal obstruction, K56.699 — Other intestinal obstruction unspecified as to partial versus complete obstruction, K56.7 — Ileus, unspecified, K59.31 — Toxic megacolon, K63.1 — Perforation of intestine (nontraumatic), K65.0 — Generalized (acute) peritonitis, K65.1 — Peritoneal abscess, K65.2 — Spontaneous bacterial peritonitis, K65.3 — Choleperitonitis, K65.8 — Other peritonitis, K65.9 — Peritonitis, unspecified, K67 — Disorders of peritoneum in infectious diseases classified elsewhere, K68.12 — Psoas muscle abscess, K68.19 — Other retroperitoneal abscess, P77.1 — Stage 1 necrotizing enterocolitis in newborn, P77.2 — Stage 2 necrotizing enterocolitis in newborn, P77.3 — Stage 3 necrotizing enterocolitis in newborn, P77.9 — Necrotizing enterocolitis in newborn, unspecified, P78.0 — Perinatal intestinal perforation, +55 more

Related risk categories

These categories interact through CMS's HCC hierarchy — one can suppress the other's risk-adjustment weight when both are present on a claim.

Intestine Transplant Status/Complications

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Peritonitis and intra-abdominal abscess).

K61.0 — Anal abscess, K61.1 — Rectal abscess, K61.2 — Anorectal abscess, K61.3 — Ischiorectal abscess, K61.31 — Horseshoe abscess, K61.39 — Other ischiorectal abscess, K61.4 — Intrasphincteric abscess, K61.5 — Supralevator abscess, K63.0 — Abscess of intestine, K65.0 — Generalized (acute) peritonitis, K65.1 — Peritoneal abscess, K65.2 — Spontaneous bacterial peritonitis, K65.3 — Choleperitonitis, K65.8 — Other peritonitis, K65.9 — Peritonitis, unspecified, K67 — Disorders of peritoneum in infectious diseases classified elsewhere, K68.11 — Postprocedural retroperitoneal abscess, K68.12 — Psoas muscle abscess, K68.19 — Other retroperitoneal abscess, K75.0 — Abscess of liver, +32 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main terms “Fibrosis, fibrotic”, “Necrosis, necrotic”, “Lipodystrophy”, …; these codes share that main term but sit in a different category of the Tabular List.

J94.1 — Fibrothorax (pleura), J98.09 — Other diseases of bronchus, not elsewhere classified (bronchus), J98.59 — Other diseases of mediastinum, not elsewhere classified (mediastinum), K04.1 — Necrosis of pulp (pulp), K13.5 — Oral submucous fibrosis (submucous), K22.89 — Other specified disease of esophagus (esophagus), K31.89 — Other diseases of stomach and duodenum (stomach), K55.049 — Acute infarction of large intestine, extent unspecified (colon), K55.069 — Acute infarction of intestine, part and extent unspecified (omentum), K62.89 — Other specified diseases of anus and rectum (anal papillae), K68.2 — Retroperitoneal fibrosis (retroperitoneal), K70.2 — Alcoholic fibrosis and sclerosis of liver (liver, alcoholic), K74.00 — Hepatic fibrosis, unspecified (liver), K74.01 — Hepatic fibrosis, early fibrosis (liver, mild), K74.02 — Hepatic fibrosis, advanced fibrosis (liver, advanced), K74.0A — Hepatic fibrosis, moderate fibrosis (liver, moderate), K74.2 — Hepatic fibrosis with hepatic sclerosis (liver, with sclerosis), K76.2 — Central hemorrhagic necrosis of liver (liver, hemorrhagic, central), K76.6 — Portal hypertension (hepatolienal), K86.89 — Other specified diseases of pancreas (pancreas), +120 more

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Gamma-glutamyl Transferase (GGT) Test

Contextual Map

Every relationship of K65.4 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run K65.4 with this related code in Claim Check

Hierarchy

• K00-K95 — Chapter 11: Diseases of the Digestive System (K00-K95) (K00-K95)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• K65-K68 — Diseases of peritoneum and retroperitoneum[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Referenced by Code Also instructions

• K57 — Diverticular disease of intestine[Code Also](via K65.-): “peritonitis (K65.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Clinical classification (CCSR)

• DIG016 — Peritonitis and intra-abdominal abscess[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

Risk adjustment (CMS-HCC)

• HCC 78 — Intestinal Obstruction/Perforation [CMS-HCC]— CMS-HCC V28 · 2026

MS-DRG Grouper

• CC — Complication or Comorbidity [MS-DRG severity]: “As a secondary diagnosis this code can raise the stay's MS-DRG severity tier (CC).”— CMS MS-DRG Definitions Manual (Appendix C) · FY2026
• DRG 393 — OTHER DIGESTIVE SYSTEM DIAGNOSES WITH MCC[MS-DRG]: “OTHER DIGESTIVE SYSTEM DIAGNOSES WITH MCC (MDC 06)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 394 — OTHER DIGESTIVE SYSTEM DIAGNOSES WITH CC[MS-DRG]: “OTHER DIGESTIVE SYSTEM DIAGNOSES WITH CC (MDC 06)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 395 — OTHER DIGESTIVE SYSTEM DIAGNOSES WITHOUT CC/MCC[MS-DRG]: “OTHER DIGESTIVE SYSTEM DIAGNOSES WITHOUT CC/MCC (MDC 06)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 791 — PREMATURITY WITH MAJOR PROBLEMS[MS-DRG]: “PREMATURITY WITH MAJOR PROBLEMS (MDC 15)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 793 — FULL TERM NEONATE WITH MAJOR PROBLEMS[MS-DRG]: “FULL TERM NEONATE WITH MAJOR PROBLEMS (MDC 15)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026

MDC crossing

• MDC 06 — Diseases and Disorders of the Digestive System[MDC crossing]: “Diseases and Disorders of the Digestive System — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 5,744 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026
• MDC 15 — Newborns and Other Neonates with Conditions Originating in Perinatal Period[MDC crossing]: “Newborns and Other Neonates with Conditions Originating in Perinatal Period — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs.”— CMS MS-DRG Definitions Manual · FY2026

Index entries (14)

• Fat, necrosis, mesentery[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Fat, necrosis, omentum[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Fibrosis, fibrotic, sclerosing mesenteric (idiopathic)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Lipodystrophy, mesenteric[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Mesenteritis, retractile[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Mesenteritis, sclerosing[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Necrosis, necrotic (ischemic), fat, fatty (generalized), abdominal wall[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Necrosis, necrotic (ischemic), fat, fatty (generalized), mesentery[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• and 6 more

Nearest codes

• K65 — Peritonitis[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• K65.0 — Generalized (acute) peritonitis[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• K65.1 — Peritoneal abscess[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• K65.2 — Spontaneous bacterial peritonitis[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• K65.3 — Choleperitonitis[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• K65.8 — Other peritonitis[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• K65.9 — Peritonitis, unspecified[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Change history

• FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Relevant guides

• Which ICD-10-CM Chapters Carry the Most Excludes1 Notes? A Census of the Tabular List →

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data

CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page

Coding guidelines Official source data

ICD-10-CM Official Guidelines for Coding and Reporting (FY2026), quoted by section Release, file and checksum · Publisher’s page

Claim edits Official source data

CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page

Inpatient payment groups Official source data

CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page

Risk adjustment Official source data

2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release Release, file and checksum · Publisher’s page

Change history and date-of-service validity Official source data

CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page

Comparisons, relationships and the contextual map MedCoder structured relationship

Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears

Summary and FAQ answers MedCoder explanation

Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Nearest Codes in This Family

Official ICD-10-CM classifications closest to K65.4 in its code family, with their registry titles.

• K65 — Peritonitis
• K65.0 — Generalized (acute) peritonitis
• K65.1 — Peritoneal abscess
• K65.2 — Spontaneous bacterial peritonitis
• K65.3 — Choleperitonitis
• K65.8 — Other peritonitis
• K65.9 — Peritonitis, unspecified

View all codes in the K65 family