2026 ICD-10-CM Diagnosis Code M05.9Rheumatoid arthritis with rheumatoid factor, unspecified
ICD-10-CM Codes›M00–M99›M05-M14›M05
- Billable — Valid for Submission
- Risk Adjusts — HCC 93
- Chronic Condition
M05.9 is a billable ICD-10-CM diagnosis code for rheumatoid arthritis with rheumatoid factor, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 545 through 547. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Rheumatoid arthritis and related disease.
For Medicare Advantage risk adjustment, M05.9 maps to CMS-HCC Category 93 (Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders) under the V28 model, adding a risk factor of about 0.617 for a community, non-dual, aged beneficiary in payment year 2026.
This medical diagnosis code is frequently used in Orthopedics medical specialties to designate conditions such rheumatoid arthritis.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
M05.9 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Anti-citrullinated protein antibody detected
- Anti-citrullinated protein antibody positive erosive rheumatoid arthritis
- Rheumatoid arthritis in remission
- Rheumatoid arthritis with erosion of joint
- Rheumatoid factor and anti-citrullinated protein antibody positive erosive rheumatoid arthritis
- Rheumatoid factor and anti-citrullinated protein antibody positive rheumatoid arthritis
- Seropositive erosive rheumatoid arthritis
- Seropositive rheumatoid arthritis
- Seropositive rheumatoid arthritis in remission
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Seropositive Rheumatoid Arthritis
rheumatoid arthritis in which a patient's serum is positive for certain disease-related antibodies including anti-cyclic citrullinated peptides (anti-ccps), also called anti-citrullinated protein antibodies (acpas),and rheumatoid factor (rf). screening for anti-ccps is more specific than rf which can be found in other pathologic conditions. the production of these disease-associated antibodies may precede the development of clinical symptoms by several years. seropositive patients have a greater likelihood of developing extra-articular complications and a more severe course of disease.
Patient EducationClinical
Rheumatoid Arthritis
Rheumatoid arthritis (RA) is a form of arthritis that causes pain, swelling, and stiffness in your joints. RA is an autoimmune disease. Although it is most common in the wrist and fingers, this disease can cause your immune system to attack any joint tissue. The inflammation (swelling) that comes with RA can also affect other body parts.
The full article covers:
- What is rheumatoid arthritis?
- Who is more likely to get rheumatoid arthritis?
- What causes rheumatoid arthritis?
- What are the symptoms of rheumatoid arthritis?
- How is rheumatoid arthritis diagnosed?
- What are the treatments for rheumatoid arthritis?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert M05.9 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code History & ChangesHistory
Replaced This code was replaced in the FY 2026 code set by:
- M05.A - Abn rheu fctr & anti-citrul protein antibody w rheu arthrit
- M05.A - Abn rheu fctr & anti-citrul protein antibody w rheu arthrit
- M05.A - Abn rheu fctr & anti-citrul protein antibody w rheu arthrit
Questions About M05.9Overview
What is the ICD-10 code for rheumatoid arthritis with rheumatoid factor, unspecified?
The ICD-10-CM code for rheumatoid arthritis with rheumatoid factor, unspecified is M05.9 (sometimes written as M059). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is M05.9 (Rheumatoid arthritis with rheumatoid factor) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report rheumatoid arthritis with rheumatoid factor, unspecified on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does M05.9 group to?
When rheumatoid arthritis with rheumatoid factor, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 545, 546, 547, with relative weights from 0.8362 to 2.4817 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of M05.9?
Under the General Equivalence Mappings, rheumatoid arthritis with rheumatoid factor, unspecified converts to ICD-9-CM 714.0 (rheumatoid arthritis). The mapping is approximate, so confirm the match fits the documentation.
What HCC is M05.9?
M05.9 (rheumatoid arthritis with rheumatoid factor, unspecified) maps to CMS-HCC Category 93 (Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders), commonly written as HCC 93, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 40 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 83.
Does M05.9 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, M05.9 adds a risk adjustment factor of about 0.617 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.288 to 0.617 depending on the payment segment). HCC 93 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 93 category page.
