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A18.31 ICD-10-CM Code: Tuberculous peritonitis

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Tabular directives
2 inclusion terms · 7 Excludes1 · 1 use-additional code

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43, Appendix B.

  • MS-DRG 371 — MAJOR GASTROINTESTINAL DISORDERS AND PERITONEAL INFECTIONS WITH MCC (MDC 06)
  • MS-DRG 372 — MAJOR GASTROINTESTINAL DISORDERS AND PERITONEAL INFECTIONS WITH CC (MDC 06)
  • MS-DRG 373 — MAJOR GASTROINTESTINAL DISORDERS AND PERITONEAL INFECTIONS WITHOUT CC/MCC (MDC 06)
  • MS-DRG 974 — HIV WITH MAJOR RELATED CONDITION WITH MCC (MDC 25)
  • MS-DRG 975 — HIV WITH MAJOR RELATED CONDITION WITH CC (MDC 25)
  • MS-DRG 976 — HIV WITH MAJOR RELATED CONDITION WITHOUT CC/MCC (MDC 25)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for A18.31 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 A18.31 itself; “inherited from” names the category or block whose note applies here.

Includes

Conditions the official ICD-10-CM tabular list includes under this code.

  • infections due to Mycobacterium tuberculosis and Mycobacterium bovis

Source: inherited from A15-A19

Inclusion Terms

Alternative terms the tabular list files under this code.

  • Tuberculous ascites

Excludes1 — Not Coded Here

Conditions generally not reported together with this code (Excludes1) -- an error unless the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Source: inherited from A15-A19

Use Additional Code

Supplementary codes the tabular list directs you to add.

  • Use additional code, if applicable, for associated cachexia (E88.A)

Source: inherited from A15-A19

Coder workflow for A18.31

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

Before you code A18.31

  1. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with A18.31. 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 A18.31’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.

    ReviewP37.0, R76.1, A15, J65, R76.11, B90

Consider A18.31. Then work the Use Additional Code 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 A18.31(7 notes)

    Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with A18.31: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

    CompareP37.0, R76.1, A15, J65, R76.11, B90

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

  • Use Additional Code — after identifying A18.31(1 note)

    Coding workflow: Check whether the documentation supports the additional code(s) the note names, and report them with A18.31 when it does. Where the instruction is conditional (“if applicable”, “if known”), it applies only when the record documents the condition.

    ReviewE88.A

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

Coding decision scenarios

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

Documentation: Both the condition A18.31 describes and a condition named in its Excludes1 note are documented for the same encounter.

Coding question: Can both codes be reported?

Path: Review the Excludes1 note and the excluded code, and look for a provider statement on whether the two conditions are related.

Reason: Excludes1 means the two are not coded together; the exception is when the record shows the conditions are unrelated to each other (Guidelines I.A.12.a).

ReviewP37.0, R76.1, A15, J65, R76.11, B90

Documentation: A condition the Use Additional Code note names is documented.

Coding question: Is a second code reported with A18.31?

Path: Review the Use Additional Code note and the code it names.

Reason: The additional code is reported when the record documents the condition; a conditional instruction applies only when its condition is met (Guidelines I.A.13).

ReviewE88.A

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.

Code Overview

Tuberculous peritonitis is a billable ICD-10-CM diagnosis code (A18.31).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Indexed Clinical Terms (9)

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.

Verify Before Coding

  • MCC 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 A18.31 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 2 Excludes1 notes: K65 — Peritonitis, K67 — Disorders of peritoneum in infectious diseases classified elsewhere.

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 1 Excludes2 note: A31 — Infection due to other mycobacteria (via A18.-).

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: MCC — Major 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 18 clinically related codes on its CMS exclusion list. Does not count toward severity when the stay groups to DRGs 974-976 (HIV with Major Related Condition).

Named in the grouper logic of 6 MS-DRGs: DRG 371 (MDC 06), DRG 372 (MDC 06), DRG 373 (MDC 06), DRG 974 (MDC 25), DRG 975 (MDC 25), DRG 976 (MDC 25).

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

Clinical classification (AHRQ CCSR):INF001 — Tuberculosis (default); DIG016 — Peritonitis and intra-abdominal abscess.

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 MCC — 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.

A17.9 — Tuberculosis of nervous system, unspecified, A18.32 — Tuberculous enteritis, A18.39 — Retroperitoneal tuberculosis, A18.82 — Tuberculosis of other endocrine glands, A18.83 — Tuberculosis of digestive tract organs, not elsewhere classified, A18.84 — Tuberculosis of heart, A18.89 — Tuberculosis of other sites, A31.2 — Disseminated mycobacterium avium-intracellulare complex (DMAC), A31.8 — Other mycobacterial infections, A31.9 — Mycobacterial infection, unspecified, A49.3 — Mycoplasma infection, unspecified site, A49.8 — Other bacterial infections of unspecified site, A49.9 — Bacterial infection, unspecified, B92 — Sequelae of leprosy, B94.2 — Sequelae of viral hepatitis, B94.8 — Sequelae of other specified infectious and parasitic diseases, B94.9 — Sequelae of unspecified infectious and parasitic disease

Same clinical category (CCSR)

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

A18.10 — Tuberculosis of genitourinary system, unspecified, A18.11 — Tuberculosis of kidney and ureter, A18.12 — Tuberculosis of bladder, A18.13 — Tuberculosis of other urinary organs, A18.14 — Tuberculosis of prostate, A18.15 — Tuberculosis of other male genital organs, A18.16 — Tuberculosis of cervix, A18.17 — Tuberculous female pelvic inflammatory disease, A18.18 — Tuberculosis of other female genital organs, A18.2 — Tuberculous peripheral lymphadenopathy, A18.32 — Tuberculous enteritis, A18.39 — Retroperitoneal tuberculosis, A18.4 — Tuberculosis of skin and subcutaneous tissue, A18.50 — Tuberculosis of eye, unspecified, A18.51 — Tuberculous episcleritis, A18.52 — Tuberculous keratitis, A18.53 — Tuberculous chorioretinitis, A18.54 — Tuberculous iridocyclitis, A18.59 — Other tuberculosis of eye, A18.6 — Tuberculosis of (inner) (middle) ear, +90 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main terms “Tuberculosis, tubercular, tuberculous”, “Peritonitis”, “Abscess”, …; these codes share that main term but sit in a different category of the Tabular List.

A15.6 — Tuberculous pleurisy (empyema), A15.7 — Primary respiratory tuberculosis (primary), A15.8 — Other respiratory tuberculosis (nose), A15.9 — Respiratory tuberculosis unspecified, A17.0 — Tuberculous meningitis (dura), A17.81 — Tuberculoma of brain and spinal cord (brain, tuberculous), A17.82 — Tuberculous meningoencephalitis (myelitis), A17.83 — Tuberculous neuritis (nerve), A17.89 — Other tuberculosis of nervous system (polyneuropathy), A17.9 — Tuberculosis of nervous system, unspecified (nervous system), A19.0 — Acute miliary tuberculosis of a single specified site (miliary, acute, single specified site), A19.1 — Acute miliary tuberculosis of multiple sites (multiple, acute), A19.2 — Acute miliary tuberculosis, unspecified (miliary, acute), A19.8 — Other miliary tuberculosis (miliary, chronic), A19.9 — Miliary tuberculosis, unspecified (miliary), A36.89 — Other diphtheritic complications (diphtheritic), A48.0 — Gas gangrene (anerobic), A50.08 — Early visceral congenital syphilis (syphilitic, congenital), A50.59 — Other late congenital syphilis, symptomatic (Dubois), A52.74 — Syphilis of liver and other viscera (syphilitic), +209 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.

Fecal Occult Blood Test (FOBT), Gamma-glutamyl Transferase (GGT) Test, HIV Screening Test, Iron Panel

Contextual Map

Every relationship of A18.31 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 A18.31 with these 3 related codes in Claim Check

Hierarchy

Referenced by Excludes1 notes

Referenced by Excludes2 notes

Clinical classification (CCSR)

MS-DRG Grouper

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 25 — Human Immunodeficiency Virus Infections[MDC crossing]: “Human Immunodeficiency Virus Infections — 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 (9)

  • Abscess (connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic), peritoneum, peritoneal (perforated) (ruptured), tuberculous[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Ascites (abdominal), tuberculous[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Peritonitis (adhesive) (bacterial) (fibrinous) (hemorrhagic) (idiopathic) (localized) (perforative) (primary) (with adhesions) (with effusion), fibrocaseous (tuberculous)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Peritonitis (adhesive) (bacterial) (fibrinous) (hemorrhagic) (idiopathic) (localized) (perforative) (primary) (with adhesions) (with effusion), tuberculous[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Tuberculosis, tubercular, tuberculous (calcification) (calcified) (caseous) (chromogenic acid-fast bacilli) (degeneration) (fibrocaseous) (fistula) (interstitial) (isolated circumscribed lesions) (necrosis) (parenchymatous) (ulcerative), abscess (respiratory), subdiaphragmatic[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Tuberculosis, tubercular, tuberculous (calcification) (calcified) (caseous) (chromogenic acid-fast bacilli) (degeneration) (fibrocaseous) (fistula) (interstitial) (isolated circumscribed lesions) (necrosis) (parenchymatous) (ulcerative), ascites[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Tuberculosis, tubercular, tuberculous (calcification) (calcified) (caseous) (chromogenic acid-fast bacilli) (degeneration) (fibrocaseous) (fistula) (interstitial) (isolated circumscribed lesions) (necrosis) (parenchymatous) (ulcerative), omentum[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Tuberculosis, tubercular, tuberculous (calcification) (calcified) (caseous) (chromogenic acid-fast bacilli) (degeneration) (fibrocaseous) (fistula) (interstitial) (isolated circumscribed lesions) (necrosis) (parenchymatous) (ulcerative), peritoneum NEC[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • and 1 more

Nearest codes (37)

Change history

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

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
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
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

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "A18.31 — Tuberculous peritonitis." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/a18.31-tuberculous-peritonitis

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Tuberculous peritonitis

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027 (effective October 1, 2026), and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to A18.31 in its code family, with their registry titles.

View all codes in the A18 family