M06.9: Rheumatoid arthritis, unspecified

The ICD-10-CM code for rheumatoid arthritis when the diagnosis is confirmed but the record does not specify serostatus or a named subtype.

Billable

FY2027

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At a glance

Code Family

M06: Other rheumatoid arthritis, within block M05-M14, inflammatory polyarthropathies, in Chapter 13, diseases of the musculoskeletal system and connective tissue.

DRG Grouping

When rheumatoid arthritis is the principal diagnosis for a medical admission, M06.9 groups to MS-DRG 545, 546 or 547, connective tissue disorders, in MDC 08 under the FY2027 MS-DRG v44 grouper. A CC or MCC on another diagnosis sets the tier within that family. A qualifying O.R. procedure moves the case to a surgical MS-DRG instead.

HCC Mapping (v28)

HCC 93: Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders.

Condition

Rheumatoid arthritis

Family Specificity

M06.9 is the unspecified code within the M06 family. The Index sends Arthritis, rheumatoid to M06.9 and Arthritis, rheumatoid, seronegative to M06.00. Confirmed seropositivity moves the encounter to the M05 family. Documented subtypes and manifestations move it to the specific M05 and M06 codes.

Effective Date

Valid in the FY2026 code set and unchanged in the FY2027 update.

Which rheumatoid arthritis code do I assign?

The RA families divide first on serostatus and then on site, subtype and systemic involvement. Documented serostatus, named subtypes and extra-articular manifestations are what move an encounter off M06.9, which is the code of last resort when none of that appears in the record. A named limb joint alone does not move it. The only site subterm directly under Arthritis, rheumatoid is spine, which the Index sends to Spondylitis, ankylosing.

When documentation says…

Code

RA with rheumatoid lung disease

M05.10-M05.19

Use when the provider documents rheumatoid lung disease with rheumatoid arthritis. The Index sends Rheumatoid, lung to M05.10 and adds a subterm for each site. The record should identify the involved site.

RA with rheumatoid vasculitis

M05.20-M05.29

Use when rheumatoid vasculitis is documented. The Index sends Rheumatoid, vasculitis to M05.20 and adds a subterm for each site.

Seropositive RA of multiple sites with no organ or system involvement

M05.79

Use when rheumatoid factor is confirmed, multiple sites are involved and no extra-articular organ or system involvement is documented. The Index sends Arthritis, rheumatoid, seropositive, without organ involvement to M05.70 when no site is named.

Abnormal rheumatoid factor and anti-CCP antibody documented with RA

M05.A

Abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis. M05.A carries a Code first note for rheumatoid arthritis with rheumatoid factor by site, if known (M05.00 to M05.8A).

RA with a negative rheumatoid factor

M06.0-

Use for rheumatoid arthritis without rheumatoid factor. The Index sends Arthritis, rheumatoid, seronegative to M06.00 and adds a subterm for each site.

Adult-onset Still's disease

M06.1

Use when the provider documents this named subtype rather than rheumatoid arthritis generally.

Rheumatoid bursitis

M06.2-

Use when rheumatoid bursitis is documented. Site options apply.

Rheumatoid nodule

M06.3-

Use when a rheumatoid nodule is documented. Site options apply.

Inflammatory polyarthropathy

M06.4

Use when inflammatory polyarthropathy is the documented diagnosis.

RA of a specified type with no code of its own

M06.8-

Other specified rheumatoid arthritis. The Index sends Arthritis, rheumatoid, specified type NEC to M06.80 and adds a subterm for each site.

RA confirmed, but serostatus and subtype absent from the note

M06.9

The unspecified residual, appropriate when the record documents rheumatoid arthritis without specifying positive or negative rheumatoid factor or a named subtype. A named limb joint without a serostatus still codes here.

Tabular notes

NO EXCLUDES1 AT M06.9

M06.9 carries no Excludes1 restrictions in the FY2027 tabular.

NO EXCLUDES2 AT M06.9

M06.9 and category M06 carry no Excludes2 note in the FY2027 tabular. Chapter 13 carries an Excludes2 list that reaches M06.9, including arthropathic psoriasis (the L40.5 codes).

NO USE ADDITIONAL, CODE ALSO OR CODE FIRST

M06.9 and category M06 carry no Use Additional, Code Also or Code First instruction. Chapter 13 carries a general note to use an external cause code following the musculoskeletal code, if applicable, to identify the cause. Rheumatoid lung disease and rheumatoid vasculitis take the M05.1 and M05.2 combination codes in place of M06.9.

FY2027 CHANGES

M06.9 is unchanged in the FY2027 update, effective 1 October 2026. The FY2027 codes addenda add, delete or revise no code in categories M05 and M06. The FY2027 tabular addenda change no note in either category.

Operational & financial impact

Why specificity matters beyond the chart: risk adjustment, DRG assignment and denial exposure all follow from which code is selected.

CMS-HCC v28 (PY2024+)

HCC 93: Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. M06.9 maps to this category in CMS-HCC Model Version 28, which is fully operative at 100% weight for Medicare Advantage payment year 2026.

Every M05 and M06 code in the v28 crosswalk maps to HCC 93 except M06.4, inflammatory polyarthropathy, which maps to HCC 94. HCC 93 sits above HCC 94 in the v28 hierarchy. M05.A is absent from the crosswalk available here, which predates it. Its mapping is indeterminate. Choosing a more specific RA code within HCC 93 improves coding accuracy without changing the HCC.

V24 TO V28

Under v24, M06.9 mapped to HCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease. Under v28 it maps to HCC 93.

MS-DRG ASSIGNMENT (FY2027, V44)

When rheumatoid arthritis is the principal diagnosis for a medical admission, M06.9 groups within MDC 08, diseases and disorders of the musculoskeletal system and connective tissue, under the FY2027 MS-DRG v44 grouper. The family is MS-DRG 545, 546 or 547, connective tissue disorders with MCC, with CC or without CC/MCC. A CC or MCC on another diagnosis sets the tier within that family. A qualifying O.R. procedure moves the case to a surgical MS-DRG instead.

MEDICARE AND PAYER COVERAGE

There is no National Coverage Determination specific to M06.9.

WHERE SPECIFICITY IS LOST

Reporting M06.9 when the record already confirms seropositive disease misstates the encounter. The Index sends Arthritis, rheumatoid, seropositive to M05.9. A rheumatoid arthritis diagnosis left undocumented in the data collection year does not count toward the payment-year risk score.

Documentation checklist to support M06.9

Chart elements that support code selection and reduce specificity-driven denials.

Provider documentation of rheumatoid arthritis as a confirmed diagnosis rather than a suspected or historical one.

Serostatus, recorded as a positive or negative rheumatoid factor result, since rheumatoid factor moves the encounter to the M05 family and a negative result supports the M06.0 codes. An abnormal anti-CCP antibody supports M05.A only with an abnormal rheumatoid factor.

The joint sites involved, which complete the site character once serostatus or a subtype is documented.

Any named subtype, such as adult-onset Still's disease, rheumatoid bursitis or rheumatoid nodule, each of which has its own code.

Systemic manifestations such as rheumatoid lung disease or vasculitis, which move the encounter to the M05.1 and M05.2 combination codes.

Documentation of the rheumatoid arthritis diagnosis within the data collection year, since M06.9 must appear in the clinical record that year to contribute to the payment-year risk score.

Evidence that rheumatoid arthritis was addressed at the encounter, whether for chronic disease management, DMARD or biologic monitoring, or evaluation of an acute flare.

Sequencing of M06.9 as the principal or primary diagnosis when rheumatoid arthritis is the reason for the encounter.

FAQ

When should M05.- be used instead of M06.9?

The M05 codes apply when the provider documents seropositive rheumatoid arthritis or rheumatoid arthritis with rheumatoid factor. The Index sends Arthritis, rheumatoid, seropositive to M05.9 and Arthritis, rheumatoid, seronegative to M06.00. M06.9 is the code for rheumatoid arthritis documented without serostatus. Reporting it when the chart confirms seropositive RA misstates the encounter.

Does documenting seropositive versus seronegative disease change the risk score?

No. The seropositive M05 codes and the seronegative M06.0 codes map to HCC 93 in the v28 crosswalk, as M06.9 does. Specificity improves coding accuracy but does not change the HCC 93 assignment.

What changed for rheumatoid arthritis between CMS-HCC v24 and v28?

M06.9 mapped to HCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease, under v24. Under v28 it maps to HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. CMS calculates 100 percent of payment year 2026 risk scores from the v28 model.

Does M06.9 carry any Excludes notes or sequencing instructions?

The FY2027 tabular carries no Excludes1, no Excludes2 and no Use Additional, Code Also or Code First instruction at M06.9 or at category M06. Chapter 13 carries an Excludes2 list and a note to use an external cause code, if applicable. Rheumatoid lung disease and rheumatoid vasculitis take the M05.1 and M05.2 combination codes in place of M06.9.

What is M05.A and does it affect M06.9?

M05.A is abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis. It sits in category M05, rheumatoid arthritis with rheumatoid factor. It carries a Code first note for rheumatoid arthritis with rheumatoid factor by site, if known (M05.00 to M05.8A). It did not change the descriptor or the notes at M06.9.

Which arthritis diagnoses should not be coded to M06.9?

Osteoarthritis belongs to the M15 through M19 series, psoriatic arthritis to the L40.5 codes, adult-onset Still's disease to M06.1, reactive arthritis to the M02 codes and juvenile arthritis to the M08 codes. Each is a distinct condition with its own code. Confirmed seropositive rheumatoid arthritis belongs to the M05 series.

How is M06.9 handled on an inpatient admission?

When rheumatoid arthritis is the principal condition for which the patient was admitted, M06.9 may be sequenced as the principal diagnosis. It groups within MDC 08, diseases and disorders of the musculoskeletal system and connective tissue, to MS-DRG 545, 546 or 547, connective tissue disorders, under the FY2027 MS-DRG v44 grouper. A CC or MCC on another diagnosis sets the tier within that family. A qualifying O.R. procedure moves the case to a surgical MS-DRG instead.

How is M06.9 used at an outpatient visit?

Code M06.9 when rheumatoid arthritis is a confirmed diagnosis addressed at the encounter, whether for chronic disease management, monitoring of DMARD or biologic therapy, or evaluation of an acute flare. Because the HCC is captured on an encounter basis, the diagnosis needs to be documented in the data collection year to count toward the payment-year risk score.

Related codes

Codes in the same family as M06.9. Only codes with a published page render as links.

Sibling codes in the M06 family

M06.0-: Rheumatoid arthritis without rheumatoid factor.
M06.1: Adult-onset Still's disease.
M06.2-: Rheumatoid bursitis.
M06.3-: Rheumatoid nodule.
M06.4: Inflammatory polyarthropathy.
M06.8-: Other specified rheumatoid arthritis.
M06.9: Rheumatoid arthritis, unspecified.

Additional codes to consider

Codes outside the M06 family considered alongside M06.9.

Companion: code alongside when documented

Z79.899: Other long term (current) drug therapy, for documented DMARD or biologic therapy.

Consider instead

M05.79: Rheumatoid arthritis with rheumatoid factor of multiple sites without organ or systems involvement, when seropositive disease of multiple sites is confirmed.
M05.A: Abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis.
M06.0-: Rheumatoid arthritis without rheumatoid factor, when a negative rheumatoid factor is documented.
M06.1: Adult-onset Still's disease.
M06.4: Inflammatory polyarthropathy.
M06.8-: Other specified rheumatoid arthritis, for a specified type of rheumatoid arthritis with no code of its own.
M15-M19: Osteoarthritis, a distinct condition that should never be coded to M06.9.
L40.50: Arthropathic psoriasis, unspecified, where the Index sends psoriatic arthritis.
M02-: Postinfective and reactive arthropathies.
M08-: Juvenile arthritis.
M08.00: Unspecified juvenile rheumatoid arthritis of unspecified site, where the Index sends juvenile rheumatoid arthritis.

Sources

All claims on this page derive from government and professional-standards sources.

National Center for Health Statistics. (2026). International classification of diseases, tenth revision, clinical modification (ICD-10-CM) FY2027 files. https://www.cdc.gov/nchs/icd/icd-10-cm/files.html
Centers for Medicare & Medicaid Services and National Center for Health Statistics. (2026). ICD-10-CM official guidelines for coding and reporting FY2027. https://ftp.cdc.gov/pub/Health_Statistics/NCHS/Publications/ICD10CM/2027/ICD-10-CM-October-1-2026-FY27-Guidelines.pdf
Centers for Medicare & Medicaid Services. (2025). 2026 model software/ICD-10 mappings. https://www.cms.gov/medicare/payment/medicare-advantage-rates-statistics/risk-adjustment/2026-model-software-icd-10-mappings
Centers for Medicare & Medicaid Services. (2026). MS-DRG classifications and software, version 44. https://www.cms.gov/medicare/payment/prospective-payment-systems/acute-inpatient-pps/ms-drg-classifications-and-software