A74.81 ICD-10-CM Code: Chlamydial peritonitis

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for A74.81 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on A74.81 itself; “inherited from” names the category or block whose note applies here.

Coder workflow for A74.81

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

Before you code A74.81

1. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with A74.81. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

   See the official tabular notes

Choose the right path

1. Does the documentation support a condition named in A74.81’s Excludes1 note?
   Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
   No → Continue.

   ReviewP39.1, P23.1, M02.3

Consider A74.81. 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).

Official instructions as workflow

• Excludes1 — check before selecting A74.81(4 notes)

  Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with A74.81: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

  CompareP39.1, P23.1, M02.3

  See the official tabular notes · Guidelines I.A.12.a

• Excludes2 — not part of A74.81(1 note)

  Coding workflow: The conditions named in this note are not included in A74.81. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

  CompareJ16.0

  See the official tabular notes · Guidelines I.A.12.b

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

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.

Indexed Clinical Terms (4)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

• Chlamydia, chlamydial, peritonitis
• Fitzhugh-Curtis syndrome, due to, Chlamydia trachomatis
• Peritonitis (adhesive) (bacterial) (fibrinous) (hemorrhagic) (idiopathic) (localized) (perforative) (primary) (with adhesions) (with effusion), chlamydial
• Syndrome, Fitzhugh-Curtis, due to, Chlamydia trachomatis

Don’t confuse A74.81 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of A74.81 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

• P39.1— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of neonatal chlamydial conjunctivitis moves the case to P39.1; the two are not reported together unless documented as unrelated.

  Full comparison: A74.81 vs P39.1 →

• P23.1— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of neonatal chlamydial pneumonia moves the case to P23.1; the two are not reported together unless documented as unrelated.

  Full comparison: A74.81 vs P23.1 →

• M02.3— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of Reiter's disease moves the case to M02.3; the two are not reported together unless documented as unrelated.

  Full comparison: A74.81 vs M02.3 →

• A55— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of sexually transmitted chlamydial diseases moves the case to A55; the two are not reported together unless documented as unrelated.

  Full comparison: A74.81 vs A55 →

• A56— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of sexually transmitted chlamydial diseases moves the case to A56; the two are not reported together unless documented as unrelated.

  Full comparison: A74.81 vs A56 →

• J16.0— Excludes2 relationship (Informational)

  Distinct conditions — both may be reported.

  A distinct condition — both may be reported when both are documented.

  What moves you there: Documentation of chlamydial pneumonia adds J16.0; it is not part of this code and both may be reported when both are documented.

  Full comparison: A74.81 vs J16.0 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Verify Before Coding

• No Medicare Code Editor or MS-DRG Definitions Manual restrictions apply to this code.

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 A74.81 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 2 Excludes1 notes: K65 — Peritonitis, K67 — Disorders of peritoneum in infectious diseases classified elsewhere.

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

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity for that release.

Named in the grouper logic of 2 MS-DRGs: DRG 865 (MDC 18), DRG 866 (MDC 18).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):DIG016 — Peritonitis and intra-abdominal abscess (default); INF003 — Bacterial infections.

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 (Peritonitis and intra-abdominal abscess, Bacterial infections).

A18.31 — Tuberculous peritonitis, A54.85 — Gonococcal peritonitis, K35.2 — Acute appendicitis with generalized peritonitis, K35.20 — Acute appendicitis with generalized peritonitis, without abscess, 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, K50.014 — Crohn's disease of small intestine with abscess, K50.114 — Crohn's disease of large intestine with abscess, K50.814 — Crohn's disease of both small and large intestine with abscess, K50.914 — Crohn's disease, unspecified, with abscess, +430 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main terms “Peritonitis”, “Chlamydia, chlamydial”; these codes share that main term but sit in a different category of the Tabular List.

A54.85 — Gonococcal peritonitis (gonococcal), A56.01 — Chlamydial cystitis and urethritis (cystitis), A56.02 — Chlamydial vulvovaginitis (vulvovaginitis), A56.09 — Other chlamydial infection of lower genitourinary tract (cervicitis), A56.11 — Chlamydial female pelvic inflammatory disease (salpingitis), A56.19 — Other chlamydial genitourinary infection (orchitis), A56.3 — Chlamydial infection of anus and rectum (proctitis), A56.4 — Chlamydial infection of pharynx (pharyngitis), A56.8 — Sexually transmitted chlamydial infection of other sites (sexually-transmitted infection NEC), A70 — Chlamydia psittaci infections (psittaci), E85.0 — Non-neuropathic heredofamilial amyloidosis (periodic, familial), K35.209 — Acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation (with or following, appendicitis, generalized), K35.30 — Acute appendicitis with localized peritonitis, without perforation or gangrene (with or following, appendicitis, localized), K35.32 — Acute appendicitis with perforation, localized peritonitis, and gangrene, without abscess (with or following, appendicitis, with perforation or rupture), K57.00 — Diverticulitis of small intestine with perforation and abscess without bleeding (with or following, diverticular disease, small intestine), K57.01 — Diverticulitis of small intestine with perforation and abscess with bleeding (with or following, diverticular disease, small intestine, with, bleeding), K57.20 — Diverticulitis of large intestine with perforation and abscess without bleeding (with or following, diverticular disease, large intestine), K57.21 — Diverticulitis of large intestine with perforation and abscess with bleeding (with or following, diverticular disease, large intestine, with, bleeding), K57.40 — Diverticulitis of both small and large intestine with perforation and abscess without bleeding (with or following, diverticular disease, large intestine, with, small intestine), K57.41 — Diverticulitis of both small and large intestine with perforation and abscess with bleeding (with or following, diverticular disease, small intestine, with, large intestine, with bleeding), +22 more

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

HIV Screening Test

Contextual Map

Every relationship of A74.81 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 A74.81 with these 2 related codes in Claim Check

Hierarchy

• A00-B99 — Chapter 1: Certain Infectious and Parasitic Diseases (A00-B99) (A00-B99)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Referenced by Excludes1 notes

• K65 — Peritonitis[Excludes1]: “peritonitis in chlamydia (A74.81)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• K67 — Disorders of peritoneum in infectious diseases classified elsewhere[Excludes1]: “peritonitis in chlamydia (A74.81)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Clinical classification (CCSR)

• DIG016 — Peritonitis and intra-abdominal abscess[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)
• INF003 — Bacterial infections[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

MS-DRG Grouper

• DRG 865 — VIRAL ILLNESS WITH MCC[MS-DRG]: “VIRAL ILLNESS WITH MCC (MDC 18)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 866 — VIRAL ILLNESS WITHOUT MCC[MS-DRG]: “VIRAL ILLNESS WITHOUT MCC (MDC 18)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026

MDC crossing

• MDC 18 — Infectious and Parasitic Diseases, Systemic or Unspecified Sites[MDC crossing]: “Infectious and Parasitic Diseases, Systemic or Unspecified Sites — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 1 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

• Chlamydia, chlamydial, peritonitis[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Fitzhugh-Curtis syndrome, due to, Chlamydia trachomatis[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Peritonitis (adhesive) (bacterial) (fibrinous) (hemorrhagic) (idiopathic) (localized) (perforative) (primary) (with adhesions) (with effusion), chlamydial[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Syndrome, Fitzhugh-Curtis, due to, Chlamydia trachomatis[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes

• A74 — Other diseases caused by chlamydiae[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• A74.0 — Chlamydial conjunctivitis[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• A74.8 — Other chlamydial diseases[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• A74.89 — Other chlamydial diseases[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• A74.9 — Chlamydial infection, unspecified[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Change history

• FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

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

Inpatient payment groups Official source data

CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 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

Nearest Codes in This Family

Official ICD-10-CM classifications closest to A74.81 in its code family, with their registry titles.

• A74 — Other diseases caused by chlamydiae
• A74.0 — Chlamydial conjunctivitis
• A74.8 — Other chlamydial diseases
• A74.89 — Other chlamydial diseases
• A74.9 — Chlamydial infection, unspecified

View all codes in the A74 family