M13.80 classifies a named arthritis type that falls outside other defined arthritis categories when the affected joint site is not documented or is not the focus of the encounter.
Verified May 8, 2026 · 5 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 5
- Region
- General
Documentation tips
What should appear in the chart to support M13.80.
Source · Editorial brief grounded in 5 cited references ↓
- Explicitly name the arthritis type in the note (e.g., 'allergic arthritis,' 'palindromic rheumatism') — M13.80 requires a 'specified' arthritis character; a vague 'arthritis NOS' may warrant a different code.
- Document why site is unspecified: state that the condition is generalized, polyarticular, or that localization was not clinically determinable at this encounter.
- Record prior workup that ruled out more specific diagnoses (rheumatoid, gout, OA, reactive, psoriatic) to justify placement in the M13.8 bucket rather than a condition-specific category.
- Note symptom duration, joint examination findings, ROM limitations, and relevant lab or imaging results (ANA, ESR, CRP, joint X-ray) to establish medical necessity.
- If the patient has a known systemic or inflammatory condition contributing to the arthritis, evaluate whether an etiology-first coding sequence applies before assigning M13.80 as the principal diagnosis.
Related CPT procedures
Procedure codes commonly billed with M13.80. Linking the right diagnosis to the right procedure is what establishes medical necessity.
Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis
Common coding pitfalls
The recurring mistakes coders make with M13.80 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Defaulting to M13.80 when the record documents a specific joint — if the chart names the shoulder, elbow, wrist, knee, ankle, or hip, a site-specific M13.8x child code is required and M13.80 is incorrect.
- Using M13.80 for osteoarthritis or arthrosis — M13 carries a Type 1 Excludes for M15-M19; those conditions must be coded from their own category regardless of how the provider phrases the diagnosis.
- Assigning M13.80 when a more precise arthritis code exists — rheumatoid (M05-M06), gout (M10), pseudogout (M11), reactive arthritis (M02), and psoriatic arthritis (L40.5x) all have dedicated codes that take precedence.
- Confusing 'other specified' with 'unspecified' — M13.80 requires the arthritis type to be identified; if the provider writes only 'arthritis, unknown type,' consider M13.10 (monoarthritis NEC, unspecified site) or M13.0 (polyarthritis, unspecified) depending on joint count.
Clinical context
Source · Editorial summary grounded in 5 cited references ↓
M13.80 is a residual code for arthritis conditions that are 'specified' in character — meaning the provider has identified a type of arthritis — but the anatomical site is either undocumented, diffuse, or not relevant to the encounter. It sits under the M13.8 (Other specified arthritis) parent and is the only child code without a joint-level qualifier. Examples of conditions coded here include allergic arthritis (a Type 1 Excludes note under M13.8 flags this as applicable) and other named arthritis types that don't map to rheumatoid arthritis (M05-M06), crystalline arthropathy (M10-M11), or osteoarthritis (M15-M19).
Use site-specific siblings — M13.811–M13.819 for shoulder, M13.821–M13.829 for elbow, M13.831–M13.839 for wrist, and so on — whenever the chart documents a lateralized joint. M13.80 is appropriate only when no single anatomical site drives the diagnosis, or when the documentation genuinely omits location. Do not use M13.80 as a shortcut when the record contains site information; that's a specificity deficiency that will flag on audit.
M13.80 falls under the broader M13 block (Other arthritis), which carries a Type 1 Excludes for arthrosis and osteoarthritis (M15-M19). Confirm the arthritis type is not better captured by a more specific code — such as psoriatic arthropathy (L40.5x), reactive arthritis (M02.-), or gout (M10.-) — before settling on M13.80.
Sibling codes
Other billable codes under M13.8 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 5 cited references ↓
01When is M13.80 the correct code instead of a site-specific M13.8x?
02Can M13.80 be used for allergic arthritis?
03Does M13.80 require a 7th character extension?
04What distinguishes M13.80 from M13.0 (Polyarthritis, unspecified)?
05Will payers accept M13.80 for an injection claim like 20610?
06How does M13.80 interact with osteoarthritis codes?
07Is M13.80 valid for the FY2026 code set?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 (effective Oct 1, 2025)
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M05-M14/M13-/M13.80
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M13.80
- 04mdclarity.comhttps://www.mdclarity.com/icd-codes/m13-80
- 05cms.govhttps://www.cms.gov/Medicare/Coding/ICD10/Downloads/2019-ICD10-Coding-Guidelines-.pdf
Mira AI Scribe
Mira AI Scribe captures the named arthritis type, the provider's rationale for not specifying a single joint site (generalized, polyarticular, or undetermined location), relevant exam findings, ROM deficits, and any lab or imaging results that exclude higher-specificity diagnoses. This prevents downcoding to an unspecified arthritis code and defends against audit queries asking why a site-specific M13.8x child code wasn't used.
See how Mira captures M13.80 documentation