2026 ICD-10-CM Diagnosis Code K35.33Acute appendicitis with perforation, localized peritonitis, and gangrene, with abscess

ICD-10-CM Codes›K00–K95›K35-K38›K35

ICD-10-CM K35.33
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

K35.33 is a billable ICD-10-CM diagnosis code for acute appendicitis with perforation, localized peritonitis, and gangrene, with abscess. 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, Gastrointestinal and biliary perforation, and Peritonitis and intra-abdominal abscess.

Code Identity

ICD-10-CM Code
K35.33
Billable Status
Yes — Valid for Submission
Code Describes
Acute appendicitis with perforation, localized peritonitis, and gangrene, with abscess
Short Description
Ac appendicitis with perf, loc peritonitis, and gangr, wbscs
Parent Code
K35.3
Acute appendicitis with localized peritonitis

Code Classification

ChapterK00–K95Diseases of the digestive system
SectionK35-K38Diseases of appendix
CategoryK35Acute appendicitis
This CodeK35.33Acute appendicitis with perforation, localized peritonitis, and gangrene, with abscess

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Abscess of appendix
  • Abscess of peritoneum
  • Acute appendicitis with peritoneal abscess
  • Acute appendicitis with peritonitis
  • Acute fulminating appendicitis
  • Acute fulminating appendicitis with perforation AND peritonitis
  • Acute gangrenous appendicitis
  • Acute gangrenous appendicitis with perforation AND peritonitis
  • Acute perforated appendicitis
  • Gangrenous appendicitis
  • Perforation of appendix
  • Pericecal abscess
  • Rupture of appendix
  • Rupture of intestine

Tabular List NotesGuidance

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

Inclusion Terms

  • (Acute) appendicitis with (peritoneal) abscess NOS
  • Ruptured appendix with localized peritonitis and abscess

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)
      • appendix
    • Abscess(connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic)
      • cecum
    • Abscess(connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic)
      • ileocecal
    • Abscess(connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic)
      • iliac (region)
        • fossa
    • Abscess(connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic)
      • periappendicular
    • Abscess(connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic)
      • pericecal
    • Abscess(connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic)
      • peritoneum, peritoneal (perforated) (ruptured)
        • with appendicitis
    • Abscess(connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic)
      • perityphlic
    • Abscess(connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic)
      • postcecal
    • Abscess(connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic)
      • subcecal
    • Abscess(connective tissue) (embolic) (fistulous) (infective) (metastatic) (multiple) (pernicious) (pyogenic) (septic)
      • vermiform appendix
    • Appendicitis(pneumococcal) (retrocecal)
      • with
        • peritoneal abscess
    • Appendicitis(pneumococcal) (retrocecal)
      • with
        • peritonitis NEC
    • Appendicitis(pneumococcal) (retrocecal)
      • with
        • peritonitis NEC
          • localized
            • with
              • perforation
                • and abscess
    • Appendicitis(pneumococcal) (retrocecal)
      • acute (catarrhal) (fulminating) (obstructive) (retrocecal) (suppurative)
        • with
          • peritoneal abscess
    • Appendicitis(pneumococcal) (retrocecal)
      • acute (catarrhal) (fulminating) (obstructive) (retrocecal) (suppurative)
        • with
          • peritonitis NEC
    • Appendicitis(pneumococcal) (retrocecal)
      • acute (catarrhal) (fulminating) (obstructive) (retrocecal) (suppurative)
        • with
          • peritonitis NEC
            • localized
              • with
                • perforation
                  • and abscess
    • Rupture, ruptured
      • cecum (with peritonitis)
        • with peritoneal abscess

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 DIG006
Gastrointestinal and biliary perforation
Default principal diagnosis: inpatient No · outpatient No
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 K35.33 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 2020–2022No changes
FY 2023RevisedCode revised
FY 2024–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About K35.33Overview

Is K35.33 (Acute appendicitis with localized peritonitis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report acute appendicitis with perforation, localized peritonitis, and gangrene, with abscess on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does K35.33 group to?

When acute appendicitis with perforation, localized peritonitis, and gangrene, with abscess 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.