ICD-10-CM · Other

M05.8A

Rheumatoid arthritis with a confirmed positive rheumatoid factor affecting a site not captured by the anatomically specific M05.8x subcodes — such as the temporomandibular joint, cricoarytenoid joint, or other atypical locations.

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 8
Region: Other

Drawn from CDCICD10DataProvidersAAPCCMS

Documentation tips

What should appear in the chart to support M05.8A.

Source · Editorial brief grounded in 5 cited references ↓

Name the specific 'other' site explicitly in the assessment — write 'seropositive RA, temporomandibular joint' or 'seropositive RA, cricoarytenoid joint,' not just 'other joint involvement.'
Record the positive rheumatoid factor lab result (RF titer, anti-CCP) with the date of the test to substantiate the 'with rheumatoid factor' component of the code.
Document current DMARD or biologic therapy and patient response, as this supports medical necessity for ongoing management and risk-adjustment (HCC) capture.
If multiple joints are involved, list each affected site separately — atypical sites coded to M05.8A should be reported alongside any standard-site M05.8x codes rather than replacing them.
Clarify disease activity status (active, in remission, stable) and any extraarticular manifestations (pulmonary, cardiac, ocular) so additional codes can be assigned and DRG severity reflects the full clinical picture.

Related CPT procedures

Procedure codes commonly billed with M05.8A. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

20610 $68.81

Aspiration and/or injection of a major joint or bursa (shoulder, hip, knee, or subacromial bursa) performed without ultrasound guidance.

20600 $56.11

Needle aspiration and/or injection of a small joint or bursa — such as a finger or toe joint — performed without ultrasound guidance.

97110 $29.06

Therapeutic exercise billed per 15-minute unit, targeting strength, endurance, range of motion, or flexibility with direct one-on-one patient contact.

99213 $95.19

Established patient office or outpatient visit requiring 20–29 minutes of total time or low-complexity medical decision-making.

99214 $135.61

Office visit for an established patient requiring moderate-complexity medical decision making (MDM), or 30–39 minutes of total provider time on the date of service.

73030 $35.74

Radiologic examination of the shoulder requiring a minimum of two views, reported as a single unit regardless of how many views are obtained.

73221 $205.08

MRI of any upper extremity joint — shoulder, elbow, or wrist — performed without contrast material.

77080 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M05.8A and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

Using M05.8A as a default 'unspecified site' code when the joint has simply not been documented — 'other specified site' requires the provider to name the site; without that, use M05.9 (RA with RF, unspecified) or query the provider.
Assigning M05.8A when the affected joint actually maps to an existing anatomical subcode (e.g., shoulder = M05.811/812, knee = M05.861/862) — review the full M05.8 subcategory before landing on M05.8A.
Failing to distinguish seropositive RA (M05.xx) from seronegative RA (M06.0x) — if RF is negative or not documented, M05.8A is incorrect regardless of the site.
Omitting secondary codes for extraarticular manifestations (e.g., rheumatoid lung disease, vasculitis, pericarditis) that affect DRG weight and risk adjustment capture.
Conflating M05.8A with M05.89, which covers multiple sites within the standard anatomical categories — M05.8A is specifically reserved for sites outside those categories.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

M05.8A applies when the treating clinician documents seropositive rheumatoid arthritis (positive RF) involving a joint or site that falls outside the standard anatomical laterality options in the M05.8 subcategory (shoulder, elbow, wrist, hand, hip, knee, ankle/foot). Classic examples include temporomandibular joint (TMJ) involvement, cricoarytenoid arthritis causing hoarseness, or involvement of the sternoclavicular or acromioclavicular joints when the provider explicitly designates these as outside routine limb-joint categories.

Do not use M05.8A as a catch-all for unspecified RA. 'Other specified site' requires the clinician to name the site in the documentation — the code demands specificity, not ambiguity. If the affected joint is bilateral and fits a standard anatomical category, use the appropriate bilateral or paired M05.8x codes instead. If RF status is negative or not documented, shift to the M06.0x series.

M05.8A groups into MS-DRGs 545–547 (Connective Tissue Disorders with/without MCC/CC), making precise documentation of comorbidities and complications critical to appropriate DRG assignment. For orthopedic practices, this code surfaces most often during preoperative workup when RA patients present for joint replacement and the primary disease manifestation is at an atypical site, or during evaluation of extraarticular RA features that affect surgical planning.

Sibling codes

Other billable codes under M05.8 (laterality / anatomic variants).

M05.89

Oth rheumatoid arthritis w rheumatoid factor mult site

M05.80

Oth rheumatoid arthritis with rheumatoid factor of unsp site

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 5 cited references ↓

01What does 'other specified site' mean for M05.8A?

It means a joint or anatomical location that the provider has explicitly named but that does not correspond to the standard bilateral options in M05.81–M05.87 (shoulder through ankle/foot). The site must be documented by name — for example, temporomandibular joint or cricoarytenoid joint. Without a named site, the code is unsupportable.

02How is M05.8A different from M05.89?

M05.89 captures seropositive RA involving multiple standard anatomical sites simultaneously. M05.8A is for a single atypical site that falls outside the standard anatomical categories altogether. They are not interchangeable.

03Can M05.8A be used for seronegative RA at an atypical site?

No. The M05 category is exclusively for RA with rheumatoid factor (seropositive). For seronegative RA at an atypical site, use M06.08 (RA without rheumatoid factor, other specified site) or the appropriate M06.0x code.

04Is M05.8A valid as a standalone diagnosis on a surgical claim?

Yes, it is a billable, specific code effective since FY2021. It can serve as the principal diagnosis on a claim when the atypical-site seropositive RA is the reason for the encounter, such as a diagnostic joint aspiration or steroid injection at the named site.

05Does M05.8A carry HCC risk-adjustment weight?

Seropositive RA codes in the M05 category map to HCC models under CMS. Accurate coding with M05.8A — supported by documented RF positivity and active treatment — ensures the diagnosis is captured for risk adjustment. Missing documentation of the RF result or DMARD therapy can result in the code being rejected during chart review.

06What CPT procedures are most commonly paired with M05.8A in an orthopedic setting?

Joint aspiration or injection (20610, 20600) at the atypical site, MRI for joint evaluation (73221), and E/M visits (99213, 99214) for ongoing disease management are the most common pairings. Imaging codes such as 73030 may apply depending on the joint documented.

07When did M05.8A first become valid for billing?

M05.8A was introduced as a new code effective October 1, 2020 (FY2021 ICD-10-CM). Claims with dates of service prior to that date require the predecessor nonspecific codes under M05.8 or M05.9.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

Mira AI Scribe

Mira AI Scribe captures the named atypical joint site, the positive RF or anti-CCP result with test date, current DMARD/biologic regimen, and disease activity status directly from the encounter note. This prevents M05.8A from being downgraded to the nonspecific M05.9 or incorrectly mapped to a standard anatomical subcode, and eliminates the audit exposure of claiming 'other specified site' without a named site in the record.

See how Mira captures M05.8A documentation