K35.209 Acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation

The ICD-10-CM code for Acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation is K35.209 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

11: Diseases of the digestive system (K00-K95)

Section

K35-K38: Diseases of appendix (K35-K38)

Category K35

20 codes (13 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to K35.209:

• Appendicitis (pneumococcal) (retrocecal) › with › peritonitis NEC › generalized
• Peritonitis (adhesive) (bacterial) (fibrinous) (hemorrhagic) (idiopathic) (localized) (perforative) (primary) (with adhesions) (with effusion) › with or following › appendicitis › generalized
• Appendicitis (pneumococcal) (retrocecal) › acute (catarrhal) (fulminating) (obstructive) (retrocecal) (suppurative) › with › peritonitis NEC › generalized

Inclusion Terms

• (Acute) appendicitis with generalized peritonitis NOS

U.S. Hospital Utilization

• An estimated 310 U.S. inpatient stays in 2023 included K35.209 among the documented diagnoses.
• 245 stays listed it as the principal diagnosis.

Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.

Official Coding Guidelines

Chapter 11 reserved for future expansion

11. Chapter 11: Diseases of the Digestive System (K00-K95) Reserved for future guideline expansion

Source: CMS — ICD-10-CM Official Guidelines for Coding and Reporting, FY2026

References

• CMS — ICD-10-CM Official Code Set and Guidelines, FY2026
• CDC/NCHS — ICD-10-CM Files and Browser Tool
• AHRQ — HCUP National Inpatient Sample, Frequencies by Diagnosis Code (2016–2023)