2027 ICD-10-CM Diagnosis Code A42.1Abdominal actinomycosis

ICD-10-CM Codes›A00–B99›A30-A49›A42

ICD-10-CM A42.1
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

A42.1 is a billable ICD-10-CM diagnosis code for abdominal actinomycosis. 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 complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 8 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Bacterial infections.

Code Identity

ICD-10-CM Code
A42.1
Billable Status
Yes — Valid for Submission
Code Describes
Abdominal actinomycosis
Short Description
Abdominal actinomycosis
Same as the full description in the CMS dataset.
Parent Code
A42
Actinomycosis

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA30-A49Other bacterial diseases
CategoryA42Actinomycosis
This CodeA42.1Abdominal actinomycosis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Abdominal actinomycosis
  • Actinomycosis of cecum
  • Actinomycotic colitis
  • Actinomycotic enteritis of intestine
  • Actinomycotic enteritis of small intestine
  • Bacterial hepatitis
  • Hepatic actinomycosis
  • Ileocecal actinomycosis
  • Typhlitis

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to A42.1: its own notes plus those printed at A42 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 Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • diseases generally recognized as communicable or transmissible

Excludes1

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

From A42 Actinomycosis applies to 8 codes

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 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.

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 INF003
Bacterial infections
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Actinomycosis

    infections with bacteria of the genus actinomyces.

Patient EducationClinical

Bacterial Infections

Bacteria are tiny organisms (living things) that have only one cell. Under a microscope, they look like balls, rods, or spirals. They can be found almost everywhere on Earth. There are lots of bacteria in and on your body. In fact, your body has about 10 times more bacteria cells than human cells.

The full article covers:

  • What are bacteria?
  • How do bacterial infections spread?
  • What are the treatments for bacterial infections?
  • Can bacterial infections be prevented?

Read the full article at MedlinePlus

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

Convert A42.1 to ICD-9-CMHistory

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

ICD-9-CM
039.2 Abdominal actinomycosis
Exact Match The mapping is direct, with no qualifiers.

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 A42.1Overview

What is the ICD-10 code for abdominal actinomycosis?

The ICD-10-CM code for abdominal actinomycosis is A42.1 (sometimes written as A421). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is A42.1 (Actinomycosis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report abdominal actinomycosis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does A42.1 group to?

When abdominal actinomycosis 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 A42.1 a CC or MCC?

CMS lists A42.1 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 8 closely related codes in its exclusion list.

Can A42.1 be reported with B47.1?

Not as a rule. The Excludes1 note at A42, which applies to A42.1, lists "actinomycetoma (B47.1)". 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).