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A55 vs A56.4

A55 (Chlamydial lymphogranuloma (venereum)) compared with A56.4 (Chlamydial infection of pharynx), from the official CMS tabular data.

Current data releases:ICD-10-CM FY2027 · ICD-10-PCS FY2027 · HCPCS October 2026 · MS-DRG v44 · Medicare Code Editor v44.0 · NCCI PTP Q4 2026 · MUE Q4 2026 · NCD code lists 2026-01 · LCD export September 28, 2026 · All releases and sources

Summary

These codes can be reported together when both conditions are documented, because A56.4 lists A55 under Excludes2, which marks them as distinct conditions.

Official rule
What is different?

The conditions named.A55 is “Chlamydial lymphogranuloma (venereum)”; A56.4 is “Chlamydial infection of pharynx”.

Registry fact

Can these codes be reported together?

Yes, when both are documented.A56.4 lists A55 under Excludes2: “chlamydial lymphogranuloma (A55)”. Excludes2 marks distinct conditions that may both be reported when both are documented.

Official ruleGuide: Excludes1 vs Excludes2

Is there an Excludes2 relationship?

Yes.A56.4’s tabular entry: “chlamydial lymphogranuloma (A55)”. The note covers A55.

Official ruleGuide: Excludes1 vs Excludes2

Nothing found in 4 other checks; 1 check does not apply
Is there an Excludes1 relationship?

None.Neither entry carries an Excludes1 note that names the other code. A55 carries 2 Excludes1 notes and A56.4 carries 4 Excludes1 notes covering other codes; the side-by-side table quotes them.

Official rule

Is one more specific?

Not comparable.The codes sit in different categories; specificity is only comparable within one category.

Is one a parent or header code?

No.Both are billable codes, and neither contains the other.

Registry fact

Are there sequencing instructions?

None.Neither entry carries a Code First or Use Additional Code note that names the other.

Official rule

Are there other coding relationships?

None found.No laterality, encounter-phase, Table of Neoplasms, Table of Drugs and Chemicals, or history-versus-active-disease relationship links these codes.

MedCoder-derived

Official rule: a tabular instructional note or a section of the ICD-10-CM Official Guidelines, quoted as published. Registry fact: the codes’ own published attributes (titles, billable status, position in the hierarchy, code set). MedCoder-derived: a reading MedCoder computes from those facts; it is not itself a rule. How to read the labels

Can these codes be reported together?

Informational

Excludes2 relationship

A56.4
Chlamydial infection of pharynx
↔
A55
Chlamydial lymphogranuloma (venereum)

What we found

Yes, when both are documented.A56.4 carries an Excludes2 note covering A55: “chlamydial lymphogranuloma (A55)”

Excludes2 marks distinct conditions — both may be reported when both are documented.

What to review

Report both only when the documentation supports both conditions; otherwise report the one documented.

Guide: Excludes1 vs Excludes2Check these on a claim

Why it matters

An Excludes2 note means the excluded condition is not part of the code above it, but a patient can have both. Report both when both are documented.

Source / rule

CMS ICD-10-CM tabular instructional notes

Official guidance behind these answers

  • Section I.A.12.b — Excludes2 · applies to: Excludes2

    A type 2 Excludes note represents “Not included here.” An excludes2 note indicates that the condition excluded is not part of the condition represented by the code, but a patient may have both conditions at the same time. When an Excludes2 note appears under a code, it is acceptable to use both the code and the excluded code together, when appropriate.

    ICD-10-CM Official Guidelines FY2027

Quoted from the ICD-10-CM Official Guidelines for Coding and Reporting in effect for the release shown. The tabular notes above are the code-level instruction; these sections are the convention that says how such a note is applied. Source document (CMS PDF) · Release and checksum

Side by side

Similar descriptions do not make codes interchangeable. The documentation and the official instructions decide which code applies.

Official descriptionDiffers
A55

Chlamydial lymphogranuloma (venereum)

A56.4

Chlamydial infection of pharynx

StatusSame for both
Billable
Excludes1Differs
Only at A55

No note of its own beyond the shared notes

Only at A56.4
  • neonatal chlamydial conjunctivitis (P39.1)
  • neonatal chlamydial pneumonia (P23.1)
Shared by both codes (2 notes)
  • nonspecific and nongonococcal urethritis (N34.1)
  • Reiter's disease (M02.3-)
Excludes2Differs
Only at A55

No note of its own beyond the shared notes

Only at A56.4
  • chlamydial lymphogranuloma (A55)
  • conditions classified to A74.-
Shared by both codes (1 note)
  • human immunodeficiency virus [HIV] disease (B20)
CategoryDiffers
A55

Is itself a category

A56.4

A56 Other sexually transmitted chlamydial diseases

ChapterSame for both

A00-B99 — Certain Infectious and Parasitic Diseases (A00-B99)

IncludesDiffers
A55
  • Climatic or tropical bubo
  • Durand-Nicolas-Favre disease
  • Esthiomene
  • Lymphogranuloma inguinale
A56.4
  • sexually transmitted diseases due to Chlamydia
  • trachomatis

No Code first, Use additional code, Code also and 7th character note at either code.

Notes are the code’s own tabular entry, quoted as published. A note that names the other code is the one the verdict above rests on. In a row that differs, each code’s own notes are listed under it, and the notes every code shares are listed once beneath them.

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Derived from the official CMS ICD-10-CM tabular data (FY2027). A coding-rule comparison, not billing advice: payer-specific edits and medical-necessity policy are outside its scope. All data sources