2026 ICD-10-CM Diagnosis Code A18.31Tuberculous peritonitis

ICD-10-CM Codes›A00–B99›A15-A19›A18

ICD-10-CM A18.31
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A18.31 is a billable ICD-10-CM diagnosis code for tuberculous peritonitis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 371 through 373, 974 through 976. Coders also document this condition as granulomatous peritonitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Peritonitis and intra-abdominal abscess and Tuberculosis.

Code Identity

ICD-10-CM Code
A18.31
Billable Status
Yes — Valid for Submission
Code Describes
Tuberculous peritonitis
Short Description
Tuberculous peritonitis
Same as the full description in the CMS dataset.
Parent Code
A18.3
Tuberculosis of intestines, peritoneum and mesenteric glands

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA15-A19Tuberculosis
CategoryA18Tuberculosis of other organs
This CodeA18.31Tuberculous peritonitis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Granulomatous peritonitis
  • Infected ascites
  • Serositis
  • Tuberculosis of intestines, peritoneum and mesenteric glands
  • Tuberculous ascites
  • Tuberculous peritonitis

Tabular List NotesGuidance

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

Inclusion Terms

  • Tuberculous ascites

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Abscess(connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic)
      • peritoneum, peritoneal (perforated) (ruptured)
        • tuberculous
    • Ascites(abdominal)
      • tuberculous
    • Peritonitis(adhesive) (bacterial) (fibrinous) (hemorrhagic) (idiopathic) (localized) (perforative) (primary) (with adhesions) (with effusion)
      • fibrocaseous (tuberculous)
    • Peritonitis(adhesive) (bacterial) (fibrinous) (hemorrhagic) (idiopathic) (localized) (perforative) (primary) (with adhesions) (with effusion)
      • tuberculous
    • Tuberculosis, tubercular, tuberculous(calcification) (calcified) (caseous) (chromogenic acid-fast bacilli) (degeneration) (fibrocaseous) (fistula) (interstitial) (isolated circumscribed lesions) (necrosis) (parenchymatous) (ulcerative)
      • abscess (respiratory)
        • subdiaphragmatic
    • Tuberculosis, tubercular, tuberculous(calcification) (calcified) (caseous) (chromogenic acid-fast bacilli) (degeneration) (fibrocaseous) (fistula) (interstitial) (isolated circumscribed lesions) (necrosis) (parenchymatous) (ulcerative)
      • ascites
    • Tuberculosis, tubercular, tuberculous(calcification) (calcified) (caseous) (chromogenic acid-fast bacilli) (degeneration) (fibrocaseous) (fistula) (interstitial) (isolated circumscribed lesions) (necrosis) (parenchymatous) (ulcerative)
      • omentum
    • Tuberculosis, tubercular, tuberculous(calcification) (calcified) (caseous) (chromogenic acid-fast bacilli) (degeneration) (fibrocaseous) (fistula) (interstitial) (isolated circumscribed lesions) (necrosis) (parenchymatous) (ulcerative)
      • peritoneum NEC
    • Tuberculosis, tubercular, tuberculous(calcification) (calcified) (caseous) (chromogenic acid-fast bacilli) (degeneration) (fibrocaseous) (fistula) (interstitial) (isolated circumscribed lesions) (necrosis) (parenchymatous) (ulcerative)
      • peritonitis

Clinical ClassificationClinical

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

CCSR DIG016
Peritonitis and intra-abdominal abscess
Default principal diagnosis: inpatient No · outpatient No
CCSR INF001
Tuberculosis
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Serositis

    inflammation of a serous membrane.

  • Tuberculous Ascites

    ascites secondary to mycobacterium tuberculosis infection.

Patient EducationClinical

Peritoneal Disorders

Your peritoneum is the tissue that lines your abdominal wall and covers most of the organs in your abdomen. A liquid, peritoneal fluid, lubricates the surface of this tissue.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert A18.31 to ICD-9-CMHistory

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

ICD-9-CM
014.00 TB peritonitis-unspec
Approximate The match is approximate rather than exact.

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 A18.31Overview

Is A18.31 (Tuberculosis of intestines, peritoneum and mesenteric glands) a billable code?

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

What MS-DRG does A18.31 group to?

When tuberculous peritonitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 371, 372, 373, 974, 975, 976, with relative weights from 0.7274 to 2.8860 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of A18.31?

Under the General Equivalence Mappings, tuberculous peritonitis converts to ICD-9-CM 014.00 (TB peritonitis-unspec). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.