What Does ICD-10 Code A69.20 Mean?
ICD-10 code A69.20 designates Lyme disease, unspecified — a billable diagnosis code used when a provider confirms or strongly suspects Lyme disease (infection by Borrelia burgdorferi) but available documentation does not identify a specific disease stage, organ system manifestation, or complication. The code falls under category A69.2 (Lyme disease) within Chapter 1 of the ICD-10-CM Official Coding Guidelines, which covers certain infectious and parasitic diseases.
Key attributes at a glance:
- Valid and billable for FY 2026 (October 1, 2025 – September 30, 2026)
- No 7th character required
- Default inpatient and outpatient assignment: Yes for both settings
- DRG grouping: MS-DRG 867/868/869 (Other Infectious and Parasitic Disease Diagnoses with MCC/CC/without CC/MCC)
- Do not include the decimal point when submitting electronically — use A6920, not A69.20
What Conditions and Diagnoses Does A69.20 Cover?
A69.20 applies when the clinical picture is consistent with Lyme disease but specificity is absent from the medical record. Appropriate clinical scenarios include:
- Tick exposure in an endemic region with systemic symptoms (fever, fatigue, myalgia, headache) and no documented erythema migrans
- Positive or equivocal Lyme serology where the provider documents Lyme disease without naming a manifestation
- Pending laboratory workup — the provider diagnoses Lyme disease clinically before confirmatory testing is complete (outpatient setting: code signs/symptoms; inpatient: confirmed diagnosis is acceptable per ICD-10-CM guidelines Section IV.H)
- Early disseminated or early localized Lyme disease when documentation does not specify neurological, cardiac, or arthritic involvement
What Does A69.20 Specifically Exclude?
When the record documents a specific Lyme disease manifestation, A69.20 must be replaced by a more precise code. Do not assign A69.20 when the following are documented:
- Lyme meningitis → A69.21
- Other neurologic disorders (facial palsy, radiculopathy, encephalopathy) → A69.22
- Lyme arthritis → A69.23
- Other specified conditions (carditis, uveitis) → A69.29
- Erythema chronicum migrans without a Lyme disease diagnosis → A69.20 may still apply if provider explicitly links it to Borrelia burgdorferi infection
When Is A69.20 the Right Code to Use?
Selecting A69.20 requires a deliberate process — it is not a default fallback. Follow these criteria:
- Confirm the treating provider has documented Lyme disease (or a synonymous term like Borrelia burgdorferi infection) as the working or confirmed diagnosis.
- Review the record for any named manifestation: joint involvement, neurological symptoms, cardiac conduction abnormalities, or ocular findings.
- If a manifestation is present and documented by the provider, select the specific A69.2x code — not A69.20.
- If no manifestation is specified or documentation is ambiguous, assign A69.20 per ICD-10-CM Official Guidelines Section I.B.5, which permits unspecified codes when specificity is not clinically determinable.
- In outpatient settings, do not code a diagnosis as confirmed based solely on a positive ELISA without provider confirmation — code the signs and symptoms instead.
How Does A69.20 Differ From A69.29?
| Feature | A69.20 — Lyme Disease, Unspecified | A69.29 — Other Conditions Associated With Lyme Disease |
|---|---|---|
| Use when | No manifestation documented at all | Manifestation present but not covered by A69.21–A69.23 |
| Clinical examples | Fever, fatigue, tick bite — no organ involvement noted | Lyme carditis, Lyme uveitis, post-treatment Lyme syndrome |
| Documentation trigger | Absence of organ-specific documentation | Provider names a specific condition not in A69.21–A69.23 |
| Audit risk | Low if documentation supports unspecified status | Higher — requires detailed clinical narrative |
| Common confusion | Used when A69.29 should apply | Underused; coders default to A69.20 inappropriately |
In practice, coders frequently encounter cases where a patient has documented fatigue and joint achiness post-treatment — a scenario that may warrant A69.29 (post-treatment Lyme disease syndrome) rather than A69.20, provided the provider explicitly names the condition.
What Documentation Is Required to Support A69.20?
What Must the Provider Document in the Clinical Notes?
The following elements must appear in the provider’s documentation to support a clean A69.20 claim:
- Explicit provider diagnosis of Lyme disease or Borrelia burgdorferi infection — coder inference from symptoms alone is not sufficient
- Clinical findings consistent with the diagnosis (tick exposure history, endemic area travel, systemic symptom description)
- Statement of disease status: active, suspected, or confirmed
- Absence of, or failure to document, specific organ system manifestation
- Treatment plan referencing Lyme disease (e.g., antibiotic prescription for B. burgdorferi infection)
Which Diagnostic or Lab Results Support This Code?
Supporting laboratory findings referenced in the record strengthen medical necessity and reduce audit exposure:
- Two-tier serology: CDC-recommended protocol — initial ELISA or EIA, followed by confirmatory Western blot (IgM and IgG)
- Positive IgM Western blot (early disease — within 4 weeks of symptom onset)
- Positive IgG Western blot (later disease — more than 4 weeks from onset)
- C6 peptide ELISA as a supplementary or standalone assay in some payer policies
- Clinical note referencing endemic tick species (Ixodes scapularis or Ixodes pacificus in the U.S.)
Note: A positive ELISA alone is insufficient for coding confirmation — the two-tier process must be referenced or the provider’s clinical rationale for bypassing it must be documented.
What Is the Documentation Standard for Inpatient vs. Outpatient Settings?
| Setting | Documentation Rule |
|---|---|
| Inpatient | Code confirmed diagnoses at discharge per ICD-10-CM guidelines Section II; A69.20 acceptable if provider documents Lyme disease without specifying manifestation |
| Outpatient | If diagnosis is not confirmed, code signs and symptoms (e.g., R50.9 fever unspecified, M79.3 panniculitis) rather than A69.20; use A69.20 only when provider clearly states diagnosis |
| ED Setting | Follow outpatient guidelines; if provider documents Lyme disease as the reason for the encounter, A69.20 is appropriate even if workup is ongoing |
How Does A69.20 Affect Medical Billing and Claims?
A69.20 is broadly covered by commercial payers, Medicare, and Medicaid when clinical criteria are met, but documentation quality directly determines reimbursement success.
Key billing considerations:
- Medical necessity must be supported by clinical documentation — payers may request records for Lyme disease claims in non-endemic states, where incidence is flagged as statistically unusual
- ICD-10-CM coding specificity rules mean that downcoding from A69.23 to A69.20 on a claim where arthritis is documented constitutes a coding error with audit consequences
- Late-stage or chronic Lyme claims are subject to heightened payer scrutiny; diagnosis of “chronic Lyme disease” is not a recognized ICD-10-CM code and should not be coded as such
What CPT or Procedure Codes Are Commonly Billed With A69.20?
| CPT Code | Description | Typical Pairing Context |
|---|---|---|
| 86618 | Antibody; Borrelia burgdorferi (Lyme disease) | Initial serologic screening |
| 86617 | Antibody; Borrelia burgdorferi, confirmatory test (e.g., Western blot) | Two-tier testing confirmation |
| 99213–99215 | Office/outpatient E&M visit | Evaluation and diagnosis encounter |
| 99223–99233 | Inpatient E&M (initial/subsequent) | Hospitalized Lyme disease cases |
| 71046 | Chest X-ray, 2 views | Cardiac evaluation in suspected disseminated disease |
Are There Any Prior Authorization or Coverage Restrictions?
- Most commercial payers cover Lyme serology under medical necessity when clinical criteria are documented
- Extended antibiotic therapy beyond standard guidelines (e.g., for “chronic Lyme disease”) is frequently not covered and may require appeals with clinical justification
- Some LCD (Local Coverage Determination) policies from Medicare Administrative Contractors restrict coverage of repeated Lyme serology panels without documented clinical rationale
- Always verify payer-specific ICD-10 coverage policies before submitting claims involving repeated laboratory testing
What Coding Errors Should You Avoid With A69.20?
The following errors are the most frequently cited during coding audit preparation and claims review:
- Assigning A69.20 when a specific manifestation is documented — if the provider notes Lyme arthritis, A69.23 is required; A69.20 creates an undercoding deficiency
- Using A69.20 for post-treatment Lyme syndrome without provider documentation — coders sometimes default to A69.20 when A69.29 is more accurate
- Coding A69.20 in outpatient settings based on lab results alone — the provider must explicitly document the diagnosis
- Omitting the decimal when submitting paper claims — submitting A69.20 on paper versus A6920 electronically is correct; mixing formats causes rejections
- Failing to query providers when documentation is ambiguous — if the record mentions symptoms consistent with Lyme disease but the provider does not name it, coders must not assume; a compliant clinical query is appropriate
What Do Auditors Look for When Reviewing Claims With A69.20?
- Provider-authenticated diagnosis statement (not coder inference from lab values)
- Evidence that two-tier serology was performed or provider rationale for clinical-only diagnosis
- Absence of more specific A69.2x codes when manifestations are present in the record
- Appropriate sequencing when Lyme disease is secondary to another principal diagnosis
- Medical necessity support for any extended antibiotic infusion therapy billed alongside
How Does A69.20 Relate to Other ICD-10 Codes?
Understanding the full A69.2 family is essential for diagnosis code specificity and audit defense.
| ICD-10 Code | Description | Relationship to A69.20 | Key Distinction |
|---|---|---|---|
| A69.2 | Lyme disease (parent category) | Parent — not separately billable | Header code only |
| A69.21 | Meningitis due to Lyme disease | Excludes A69.20 | Requires CSF findings + provider documentation |
| A69.22 | Other neurologic disorders in Lyme disease | Excludes A69.20 | Covers facial palsy, radiculopathy, encephalopathy |
| A69.23 | Arthritis due to Lyme disease | Excludes A69.20 | Joint inflammation documented by provider |
| A69.29 | Other conditions associated with Lyme disease | Excludes A69.20 | Named manifestation outside A69.21–A69.23 |
| A69.1 | Other Vincent’s infections | Same parent category (A69) | Unrelated — oral/dental spirochetal infection |
| Z86.19 | Personal history of other infectious diseases | Use additional code | History of resolved Lyme disease |
What Is the Correct Code Sequencing When A69.20 Appears With Other Diagnoses?
- When Lyme disease is the principal or first-listed diagnosis, sequence A69.20 first, followed by any symptomatic or complication codes.
- When Lyme disease is an underlying etiology causing a manifestation coded elsewhere (e.g., cardiac arrhythmia), sequence A69.20 as the etiology; follow with the manifestation code and any “use additional code” instruction.
- When the patient presents for a follow-up visit after resolved Lyme disease, use Z09 (encounter for follow-up examination) as the first-listed code with Z86.19 as appropriate — do not reassign A69.20 if the infection is resolved.
- Never sequence A69.20 as secondary when the Lyme disease itself is the primary reason for the encounter.
Real-World Coding Scenario — How A69.20 Is Applied in Practice
Patient Encounter: A 38-year-old female presents to her primary care physician after returning from a hiking trip in Connecticut. She reports three weeks of fatigue, diffuse joint aching, headache, and low-grade fever. She recalls a possible tick attachment on her leg two weeks prior. The provider documents: “Presentation consistent with Lyme disease. Two-tier serology ordered. Starting empiric doxycycline pending results. No rash observed, no focal neurological deficits, no cardiac symptoms noted.”
Correct Code Application
- A69.20 — Lyme disease, unspecified: The provider explicitly names Lyme disease as the diagnosis. No organ-specific manifestation is documented. Two-tier testing is ordered but not yet resulted. A69.20 is the precise and defensible code.
- Supporting codes as applicable: R50.9 (fever), M79.1 (myalgia) — may be omitted if provider treats them as integral to the Lyme diagnosis
Common Mistake in This Scenario
- Incorrect code: A69.23 (Lyme arthritis) — some coders see “joint aching” and default to the arthritis code. However, Lyme arthritis requires the provider to document arthritis as a manifestation, not merely patient-reported joint pain. Assigning A69.23 without that documentation constitutes overcoding and creates audit exposure.
- Second common error: Coding only symptoms (M79.1 + R50.9) in an outpatient setting without recognizing that the provider has explicitly confirmed a Lyme disease diagnosis — A69.20 should be assigned.
Frequently Asked Questions About ICD-10 Code A69.20
Is ICD-10 Code A69.20 Valid for Use in FY 2026?
ICD-10 code A69.20 is a valid, billable diagnosis code for fiscal year 2026 with no changes to its description or status since its introduction in FY 2016. Coders should verify annually against the ICD-10-CM Official Coding Guidelines released by CMS each October, as updates to the A69 category could affect code specificity requirements.
When Should I Use A69.20 Instead of A69.29?
Use A69.20 when the provider documents Lyme disease without naming any specific manifestation or associated condition. Use A69.29 when the provider documents a named Lyme disease complication — such as post-treatment Lyme disease syndrome, Lyme carditis, or Lyme uveitis — that is not covered by A69.21, A69.22, or A69.23.
Can A69.20 Be Used When Lab Results Are Pending?
In an inpatient setting, yes — if the provider documents Lyme disease as the confirmed diagnosis at or before discharge, A69.20 may be assigned even if laboratory results are still pending. In an outpatient setting, if the provider states the diagnosis, A69.20 is appropriate; if the diagnosis remains uncertain, coders must instead report signs and symptoms per ICD-10-CM outpatient coding guidelines Section IV.
What Is the Difference Between A69.20 and A69.23?
A69.20 is used when Lyme disease is documented without specification of any manifestation. A69.23 requires the provider to explicitly document Lyme arthritis or joint inflammation as a defined complication of Borrelia burgdorferi infection — patient-reported joint pain alone does not support A69.23.
Does Medicare Cover Claims Submitted With A69.20?
Medicare covers A69.20 claims when medical necessity is supported by clinical documentation. Claims involving non-endemic regions, repeated serologic testing, or extended antibiotic infusion therapy may be subject to additional scrutiny or LCD restrictions depending on the Medicare Administrative Contractor jurisdiction.
Is “Chronic Lyme Disease” Coded as A69.20?
No. “Chronic Lyme disease” is not a recognized ICD-10-CM diagnosis and should not be coded as A69.20 or any A69.2x code without a clinically documented basis. If a provider documents post-treatment Lyme disease syndrome with persistent symptoms, the appropriate code is A69.29, provided the documentation clearly supports this specific clinical entity.
Key Takeaways
Every coder working with A69.20 should keep these principles in hand:
- A69.20 requires an explicit provider diagnosis — never assign it based solely on lab results or symptom pattern
- When any specific manifestation is documented, select A69.21–A69.29 over A69.20; using A69.20 in that context is an undercoding deficiency
- The two-tier serology protocol (ELISA + Western blot) is the CDC standard; documentation of this process supports both the diagnosis and audit defense
- In outpatient encounters, code signs and symptoms if the Lyme disease diagnosis is not confirmed by the provider at the time of the visit
- A69.29 — not A69.20 — is the appropriate code for post-treatment Lyme disease syndrome when the provider names the condition
- Submit A6920 (without decimal) on electronic claims to avoid HIPAA transaction rejections
- Review CDC Lyme disease surveillance data and CMS ICD-10-CM code updates annually to stay current with evolving coverage and coding standards
For related guidance, review medical billing documentation requirements for infectious disease diagnoses and consult coding audit preparation resources specific to Category A69 claims.
External references: CMS ICD-10-CM code files and guidelines | CDC Lyme Disease surveillance and diagnosis resources | WHO ICD-10 classification reference | AHA Coding Clinic guidance for infectious disease coding