2026 ICD-10-CM Diagnosis Code K35.31Acute appendicitis with localized peritonitis and gangrene, without perforation

ICD-10-CM Codes›K00–K95›K35-K38›K35

ICD-10-CM K35.31
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

K35.31 is a billable ICD-10-CM diagnosis code for acute appendicitis with localized peritonitis and gangrene, without perforation. 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. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Appendicitis and other appendiceal conditions and Peritonitis and intra-abdominal abscess.

Code Identity

ICD-10-CM Code
K35.31
Billable Status
Yes — Valid for Submission
Code Describes
Acute appendicitis with localized peritonitis and gangrene, without perforation
Short Description
Acute appendicitis with loc peritonitis and gangr, w/o perf
Parent Code
K35.3
Acute appendicitis with localized peritonitis

Code Classification

ChapterK00–K95Diseases of the digestive system
SectionK35-K38Diseases of appendix
CategoryK35Acute appendicitis
This CodeK35.31Acute appendicitis with localized peritonitis and gangrene, without perforation

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.

    • Appendicitis(pneumococcal) (retrocecal)
      • with
        • gangrene
          • with localized peritonitis
    • Appendicitis(pneumococcal) (retrocecal)
      • with
        • peritonitis NEC
          • localized
            • with
              • gangrene
    • Appendicitis(pneumococcal) (retrocecal)
      • acute (catarrhal) (fulminating) (obstructive) (retrocecal) (suppurative)
        • with
          • peritonitis NEC
            • localized
              • with
                • gangrene
    • Appendicitis(pneumococcal) (retrocecal)
      • acute (catarrhal) (fulminating) (obstructive) (retrocecal) (suppurative)
        • specified NEC
          • with gangrene
            • with localized peritonitis
    • Gangrene, gangrenous(connective tissue) (dropsical) (dry) (moist) (skin) (ulcer)
      • appendix
        • with
          • peritonitis, localized

Clinical ClassificationClinical

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

CCSR DIG009
Appendicitis and other appendiceal conditions
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR DIG016
Peritonitis and intra-abdominal abscess
Default principal diagnosis: inpatient No · outpatient No

Patient EducationClinical

Appendicitis

The appendix is a small, tube-like organ attached to the first part of the large intestine. It is located in the lower right part of the abdomen. It has no known function. A blockage inside of the appendix causes appendicitis. The blockage leads to increased pressure, problems with blood flow, and inflammation.

Read the full article at MedlinePlus

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

Code History & ChangesHistory

Replacement K35.31 replaces the following previously assigned code(s):

  • K35.3 - Acute appendicitis with localized peritonitis
FY 2019AddedAdded to the ICD-10-CM code setEffective October 1, 2018.
FY 2020–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About K35.31Overview

Is K35.31 (Acute appendicitis with localized peritonitis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report acute appendicitis with localized peritonitis and gangrene, without perforation on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does K35.31 group to?

When acute appendicitis with localized peritonitis and gangrene, without perforation is the principal diagnosis on an inpatient stay, it groups to MS-DRG 371, 372, 373, with relative weights from 0.7274 to 1.7731 depending on complications. Higher weights mean higher Medicare reimbursement.

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.