2026 ICD-10-CM Diagnosis Code M05.AAbnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis
M05.A is a billable ICD-10-CM diagnosis code for abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis. 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.
Code Identity
Code Classification
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Code First
Certain conditions have both an underlying etiology and multiple body system manifestations due to the underlying etiology. For such conditions, the ICD-10-CM has a coding convention that requires the underlying condition be sequenced first followed by the manifestation. Wherever such a combination exists, there is a "use additional code" note at the etiology code, and a "code first" note at the manifestation code. These instructional notes indicate the proper sequencing order of the codes, etiology followed by manifestation.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
- Abnormal, abnormality, abnormalities - See Also: Anomaly;
External Cause of Injuries IndexGuidance
References for this code in the External Cause of Injuries Index.
- Abnormal, abnormality, abnormalities
- rheumatoid factor and anti-citrullinated protein antibody
- with rheumatoid arthritis
Code History & ChangesHistory
New Code M05.A was added to the ICD-10-CM code set for FY 2026, effective October 1, 2025.
Replacement M05.A replaces the following previously assigned code(s):
- M05.9 - Rheumatoid arthritis with rheumatoid factor, unspecified
Questions About M05.AOverview
Is M05.A (Rheumatoid arthritis with rheumatoid factor) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does M05.A group to?
When abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis 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.
