2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

A18.31 is a billable ICD-10-CM diagnosis code for tuberculous peritonitis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 371 through 373, 974 through 976. 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 18 closely related codes. 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
  • Tuberculosis of intestine
  • Tuberculosis of intestines, peritoneum and mesenteric glands
  • Tuberculous ascites
  • Tuberculous mesenteric adenitis
  • Tuberculous peritonitis

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to A18.31: its own notes plus those printed at block A15-A19 and Chapter 1. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From Block A15-A19 Tuberculosis applies to 51 codes
  • infections due to Mycobacterium tuberculosis and Mycobacterium bovis
From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • diseases generally recognized as communicable or transmissible

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • Tuberculous ascites

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From Block A15-A19 Tuberculosis applies to 51 codes
  • congenital tuberculosis (P37.0)
  • nonspecific reaction to test for tuberculosis without active tuberculosis (R76.1-)
  • pneumoconiosis associated with tuberculosis, any type in A15 (J65)
  • positive PPD (R76.11)
  • positive tuberculin skin test without active tuberculosis (R76.11)
  • sequelae of tuberculosis (B90.-)
  • silicotuberculosis (J65)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • carrier or suspected carrier of infectious disease (Z22.-)
  • certain localized infections - see body system-related chapters
  • infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
  • infectious and parasitic diseases specific to the perinatal period (P35-P39)
  • influenza and other acute respiratory infections (J00-J22)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Block A15-A19 Tuberculosis applies to 51 codes
  • code, if applicable, for associated cachexia (E88.A)
From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • code to identify resistance to antimicrobial drugs (Z16.-)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name A18.31, its category, or a range that includes it.

Applicable To 1

These notes mention A18.31.

  • O98.0 Tuberculosis complicating pregnancy, childbirth and the puerperium
    Conditions in A15-A19 names A15-A19, which includes this code

Excludes1 2

These codes carry an Excludes1 note naming A18.31: they are not reported together with it, unless the two conditions are unrelated.

  • K65 Peritonitis
    peritonitis in tuberculosis (A18.31)
  • K67 Disorders of peritoneum in infectious diseases classified elsewhere
    peritonitis in tuberculosis (A18.31)

Excludes2 1

These codes carry an Excludes2 note naming A18.31: its condition is not part of those codes, and both may be reported when the patient has both.

  • A31 Infection due to other mycobacteria
    tuberculosis (A15-A19) names A15-A19, which includes this code

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 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

  • Peritonitis, Tuberculous

    a form of peritonitis seen in patients with tuberculosis, characterized by lesion either as a miliary form or as a pelvic mass on the peritoneal surfaces. most patients have ascites, abdominal swelling, abdominal pain, and other systemic symptoms such as fever; weight loss; and anemia.

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About A18.31Overview

What is the ICD-10 code for tuberculous peritonitis?

The ICD-10-CM code for tuberculous peritonitis is A18.31 (sometimes written as A1831). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

What MS-DRG does A18.31 group to?

When tuberculous peritonitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 372, 974, 976, 975, 371, 373, with relative weights from 0.6945 to 3.0488 depending on complications. Higher weights mean higher Medicare reimbursement.

Is A18.31 a CC or MCC?

CMS lists A18.31 as an MCC (major complication or comorbidity) for FY 2027. 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 18 closely related codes in its exclusion list.

Can A18.31 be reported with P37.0?

Not as a rule. The Excludes1 note at block A15-A19, which applies to A18.31, lists "congenital tuberculosis (P37.0)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).