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K35.20 ICD-10-CM Code: Acute appendicitis with generalized peritonitis, without abscess

Billing Status: NO. This is a clinician non-billable / parent hierarchy grouping in the ICD-10-CM system.

Coder workflow for K35.20

MedCoder structured workflow — derived from this code’s own official record

Before you code K35.20

  1. K35.20 is not reportable as written. Select the more specific code beneath it that the documentation supports. Codes are reported to the highest level of specificity the classification provides (Guidelines I.B.2).

    ReviewK35.200, K35.201, K35.209

    See the relationships section · Guide: How to choose an ICD-10-CM code →

Choose the right path

  1. Does the documentation support one of the more specific codes beneath K35.20?
    Yes → Select that code and continue the checks below on its own page.
    No → K35.20 cannot be reported as written; query for the specificity its subcategory needs.

    ReviewK35.200, K35.201, K35.209

Consider K35.20. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
Acuity
Acute or chronic as documented; when both are documented and separate codes exist, both are reported with the acute code first (Guidelines I.B.8).
The associated condition or complication
Whether the associated condition the title names is documented; the “with” convention presumes some links, and a provider statement that the conditions are unrelated defeats it (Guidelines I.A.15).

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Code Overview

Acute appendicitis with generalized peritonitis, without abscess is a non-billable ICD-10-CM category code (K35.20). A more specific billable subcode must be selected for claims submission.

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Verify Before Coding

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name K35.20 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 3 Excludes1 notes: K37 — Unspecified appendicitis (via K35.2.-), K65 — Peritonitis (via K35.-), K65 — Peritonitis (via K35.2.-).

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 1 Excludes2 note: K63.1 — Perforation of intestine (nontraumatic) (via K35.2.-).

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

Clinical classification (AHRQ CCSR):DIG009 — Appendicitis and other appendiceal conditions (default); DIG016 — Peritonitis and intra-abdominal abscess.

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical categories (Appendicitis and other appendiceal conditions, Peritonitis and intra-abdominal abscess).

A18.31 — Tuberculous peritonitis, A54.85 — Gonococcal peritonitis, A74.81 — Chlamydial peritonitis, K35.2 — Acute appendicitis with generalized peritonitis, K35.200 — Acute appendicitis with generalized peritonitis, without perforation or abscess, K35.201 — Acute appendicitis with generalized peritonitis, with perforation, without abscess, K35.209 — Acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation, K35.21 — Acute appendicitis with generalized peritonitis, with abscess, K35.210 — Acute appendicitis with generalized peritonitis, without perforation, with abscess, K35.211 — Acute appendicitis with generalized peritonitis, with perforation and abscess, K35.219 — Acute appendicitis with generalized peritonitis, with abscess, unspecified as to perforation, K35.3 — Acute appendicitis with localized peritonitis, K35.30 — Acute appendicitis with localized peritonitis, without perforation or gangrene, K35.31 — Acute appendicitis with localized peritonitis and gangrene, without perforation, K35.32 — Acute appendicitis with perforation, localized peritonitis, and gangrene, without abscess, K35.33 — Acute appendicitis with perforation, localized peritonitis, and gangrene, with abscess, K35.80 — Unspecified acute appendicitis, K35.89 — Other acute appendicitis, K35.890 — Other acute appendicitis without perforation or gangrene, K35.891 — Other acute appendicitis without perforation, with gangrene, +44 more

Contextual Map

Every relationship of K35.20 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run K35.20 with these 3 related codes in Claim Check

Hierarchy

Referenced by Excludes1 notes

  • K37 — Unspecified appendicitis[Excludes1](via K35.2.-): “unspecified appendicitis with peritonitis (K35.2-, K35.3-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
  • K65 — Peritonitis[Excludes1](via K35.-): “peritonitis with or following appendicitis (K35.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
  • K65 — Peritonitis[Excludes1](via K35.2.-): “acute appendicitis with generalized peritonitis (K35.2-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Excludes2 notes

Clinical classification (CCSR)

Nearest codes (19)

Change history (2)

Common coding questions

Can K35.20 be billed directly?

No. K35.20 (Acute appendicitis with generalized peritonitis, without abscess) is a non-billable ICD-10-CM category code. A more specific billable subcode must be selected based on clinical documentation.

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "K35.20 — Acute appendicitis with generalized peritonitis, without abscess." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/k35.20-acute-appendicitis-with-generalized-peritonitis-without-abscess

Change history

  • FY2024 — October 1, 2023
    Became a non-billable header
    FY2024 changes
  • FY2019 — October 1, 2018
    Added to the code set
    Acute appendicitis with generalized peritonitis, without abscess
    FY2019 changes

Nearest Codes in This Family

Official ICD-10-CM classifications closest to K35.20 in its code family, with their registry titles.

View all codes in the K35 family