ICD-10 Code A55: Chlamydial Lymphogranuloma (Venereum)

Key Takeaways

ICD-10 Code A55 is a billable diagnosis code for Chlamydial lymphogranuloma (venereum), caused by Chlamydia trachomatis serovars L1, L2, and L3

Inclusion terms for A55 include Durand-Nicolas-Favre disease, esthiomene, and lymphogranuloma inguinale – all refer to the same condition

A55 excludes other chlamydial diseases under A56 (Type 1 Excludes), so these codes can never be assigned together for the same encounter

Pabau’s clinical records system and claims management software help sexual health clinics capture A55 accurately at the point of care

Most claims errors involving sexually transmitted infection diagnoses trace back to one root cause: providers and coders using the wrong code from a closely clustered group of chlamydial disease codes. ICD-10 Code A55 sits in a tight neighborhood alongside A56 and A64, and mixing them up results in denials, audit flags, and incomplete public health reporting. According to the Centers for Medicare and Medicaid Services (CMS), accurate diagnosis coding underpins both reimbursement and surveillance integrity. This reference covers the definition, classification hierarchy, inclusion and exclusion terms, documentation requirements, and related codes for A55.

Lymphogranuloma venereum (LGV) is a notifiable disease in both the United States and the United Kingdom. That means accurate A55 assignment carries public health obligations beyond the claim itself. Getting the code right protects the patient record, satisfies payer requirements, and feeds accurate surveillance data to the CDC and UK Health Security Agency (UKHSA).

ICD-10 Code A55: definition and clinical description

ICD-10 Code A55 is the billable ICD-10-CM diagnosis code for Chlamydial lymphogranuloma (venereum). It captures a specific systemic STI caused by invasive serovars of Chlamydia trachomatis, distinct from the more common urogenital chlamydia infections that fall under A56.

The pathogen responsible for LGV is Chlamydia trachomatis, but specifically serovars L1, L2, and L3, as CDC/NCHS ICD-10-CM guidance confirms. These invasive L-serovars differ biologically from the non-invasive D-K serovars that cause common urogenital chlamydia. The L-serovars spread to regional lymph nodes and can cause chronic, destructive inflammation without treatment, making accurate coding essential for clinical management. Sexual health providers using a clinical records system that supports STI-specific documentation can capture serovar information directly in the encounter note, supporting both the code assignment and downstream audit requirements.

Classification hierarchy for A55

ICD-10 Code A55 sits within the following hierarchy in the ICD-10-CM tabular list:

Because A55 has no further subdivisions, it is always the final code assignment. There is no A55.0 or A55.1. Coders should never assign a truncated or parent-only version; A55 itself is the correct and complete code.

Inclusion terms and applicable synonyms for ICD-10 Code A55

The ICD-10-CM tabular list includes several inclusion terms under A55. These are not separate codes; they are all valid clinical synonyms for the same condition and map directly to A55.

• Durand-Nicolas-Favre disease – the historical eponym for LGV, named after the three physicians who first described the syndrome in 1913
• Esthiomene – a late-stage manifestation of LGV causing chronic ulcerative inflammation and fibrosis of the genitalia
• Lymphogranuloma inguinale – an older descriptive term emphasizing the inguinal lymphadenopathy characteristic of LGV

If a provider documents any of these terms in the encounter note, the correct code is A55. Coders working in sexual health clinic software environments should configure these synonyms as ICD-10 search aliases so that provider documentation flows cleanly to the right code without manual lookup every time.

Excludes notes and coding boundaries for A55

ICD-10 Code A55 carries a Type 1 Excludes note for A56 (Other sexually transmitted chlamydial diseases). This is the most important boundary rule for coders working in sexual health settings.

A Type 1 Excludes note means the two codes are mutually exclusive. They cannot be assigned together for the same encounter because they represent fundamentally different conditions, even though both involve Chlamydia trachomatis. A55 captures invasive LGV (L-serovars); A56 captures non-invasive common chlamydial infections (D-K serovars) affecting the lower genitourinary tract, pharynx, rectum, and other sites.

A55 vs. A56: key coding distinctions

A64 (Unspecified sexually transmitted disease) should not be used when clinical documentation is sufficient to support A55. Defaulting to A64 because it feels safer is a documentation failure, not a coding solution. Payers and auditors are giving closer attention to A64 usage as a flag for insufficient specificity. Avoid it when the encounter meets A55 criteria. Review related ICD-10 diagnosis codes in nearby sections, which address comparable specificity decisions.

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Documentation requirements when using ICD-10 Code A55

Accurate A55 coding starts with the clinical note, not the billing system. Providers need to document enough to support both the specific code and the public health reporting that follows.

The note should cover three things. First, describe symptoms consistent with LGV: swollen, tender groin lymph nodes (bubo formation), genital or anal sores, or proctocolitis in higher-risk patients. Second, record lab confirmation when you have it — specifically a positive NAAT result for Chlamydia trachomatis. Third, explain how you connected that positive result to the LGV-specific presentation, rather than treating it as just a routine chlamydia screen.

Laboratory coding for LGV encounters

Two CPT codes commonly pair with A55 on LGV encounters:

• CPT 87110 (chlamydia culture) – used when the lab performs culture-based confirmation, though NAAT has largely replaced culture in most US clinical settings
• CPT 87491 (Chlamydia trachomatis NAAT) – the standard molecular test for chlamydia, including LGV; this is the test most labs run

Note that a positive CPT 87491 result alone does not confirm LGV. Standard NAAT testing detects Chlamydia trachomatis broadly, including both LGV and non-LGV serovars. Serovar typing or an LGV-specific NAAT distinguishes L-serovar from D-K serovar infection. The provider’s clinical judgment, drawing on presentation and epidemiology, determines whether A55 or A56 is the appropriate code when the lab cannot confirm the serovar. Providers should document this reasoning explicitly in the note to support the coding decision. Maintaining HIPAA-compliant documentation practices matters especially for STI encounters, where patient privacy and reporting obligations intersect.

Stage-specific documentation for A55

LGV presents in three clinical stages, and documentation of the stage supports coding specificity and justifies treatment decisions to payers:

• Primary stage (days 3-30): small painless papule or ulcer at the inoculation site, often missed or self-healed before presentation
• Secondary stage (weeks 2-6): inguinal or femoral lymphadenopathy, often unilateral, with possible bubo formation and systemic symptoms including fever and malaise
• Tertiary stage (months to years if untreated): genital elephantiasis, esthiomene, rectal stricture, or fistulae in untreated or inadequately treated cases

Documentation that names the stage and describes the anatomical involvement gives auditors and payers the clinical context they need to adjudicate the claim. Vague notes like “LGV, treated” are technically sufficient for the code but leave the practice exposed during retrospective review. Robust ICD-10 coding documentation practices, as outlined in the ICD-10 coding documentation practices guidance Pabau publishes for clinical teams, follow the same specificity principle across all diagnostic code categories.

Related codes to use alongside ICD-10 Code A55

A55 is rarely the only code on an LGV encounter. Several additional codes support complete and accurate claim submission.

Screening and encounter context codes

Z11.3 (Encounter for screening for infections with a predominantly sexual mode of transmission) applies when a patient presents for STI screening and LGV emerges incidentally. It should not be used as the primary code when the provider establishes an active LGV diagnosis; A55 takes priority in that scenario.

Differential and co-occurring STI codes

Providers working in sexual health settings regularly encounter co-infections. A55 may appear alongside codes from the following categories, provided the provider documents each condition independently:

• A57 (Chancroid) – an ulcerative STI caused by Haemophilus ducreyi; clinically similar presentation but a different organism and a different code
• A58 (Granuloma inguinale) – also known as donovanosis; causes progressive genital ulceration, driven by Klebsiella granulomatis
• A64 (Unspecified STD) – used only when documentation is insufficient to support a specific code; avoid when the encounter meets A55 criteria

A55, A57, and A58 can all be assigned in the same encounter if the documentation supports each diagnosis. They do not exclude each other. Practices with robust claims management software can map these multi-code encounters correctly and flag any conflicting code combinations before submission, reducing denial rates on complex STI claims.

ICD-10-CM code range context for A55

The AAPC Codify ICD-10-CM lookup provides a searchable reference for the full A50-A64 block, including inclusion notes and excludes relationships for each code in the sexually transmitted diseases range.

Public health reporting obligations for LGV coded as A55

LGV is a notifiable condition in both the United States and the United Kingdom. Coding a patient encounter with A55 triggers a reporting obligation that extends beyond the payer claim.

In the US, providers must report LGV to the relevant state health department under the CDC’s nationally notifiable disease surveillance framework. Reporting timelines and methods vary by state, but most require submission within 24-72 hours of diagnosis confirmation. The WHO ICD-10 classification browser provides the international reference framework that aligns US ICD-10-CM coding with global surveillance systems, supporting cross-border epidemiological tracking of LGV outbreaks.

In the UK, LGV is notifiable under the Public Health (Control of Disease) Act. The UK Health Security Agency (UKHSA) publishes annual LGV surveillance data, and clinical coders and sexual health providers feed into it through accurate A55 coding. NHS coding standards follow the WHO ICD-10 edition, so A55 maps directly across both systems. Practices that use digital clinical forms with built-in notifiable disease prompts can flag encounters at the point of documentation, reducing the risk of missing a reporting obligation when the clinical workload is high.

Conclusion

ICD-10 code A55 identifies a specific, invasive STI that stands apart from routine chlamydial infections. Getting it right depends on three things: documentation that clearly distinguishes LGV from other chlamydial and ulcerative STIs, correctly applying the Type 1 Excludes relationship with A56, and recognizing the public health reporting duties that come with the diagnosis.

Pabau’s integrated practice management platform helps sexual health and STI-focused clinics build these coding steps directly into the consultation process. From structured clinical notes to automated claim checks, every feature works to close the gap between the clinical encounter and accurate code submission. Book a demo to see how Pabau handles STI coding workflows end to end.

Continue your research

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