ICD-10-CM 2027 diagnosis code
M05.AAbnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis
M05.A is a valid, billable ICD-10-CM code for abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.Short description: Abn rheu fctr & anti-citrul protein antibody w rheu arthrit
Code last changed in FY2026 (effective October 1, 2025). Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data
About M05.A
M05.A is the ICD-10-CM diagnosis code for abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis. It belongs to category M05 (rheumatoid arthritis with rheumatoid factor), block M05-M14 (inflammatory polyarthropathies) and chapter 13 (diseases of the musculoskeletal system and connective tissue). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.
Within M05 (rheumatoid arthritis with rheumatoid factor), M05.A is specifically for abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis. Related codes cover Felty's syndrome (M05.0), rheumatoid lung disease with rheumatoid arthritis (M05.1), rheumatoid vasculitis with rheumatoid arthritis (M05.2), rheumatoid heart disease with rheumatoid arthritis (M05.3), rheumatoid myopathy with rheumatoid arthritis (M05.4), rheumatoid polyneuropathy with rheumatoid arthritis (M05.5), rheumatoid arthritis with involvement of other organs and systems (M05.6), without organ or systems involvement (M05.7) and 2 more.
Code first: rheumatoid arthritis with rheumatoid factor by site, if known (M05.00 to M05.8A).
It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.
In MS-DRG v44.0, it is part of the grouping logic for DRG 545 (Connective Tissue Disorders with MCC, relative weight 2.3892), DRG 546 (Connective Tissue Disorders with CC, relative weight 1.1745) and DRG 547 (Connective Tissue Disorders without CC/MCC, relative weight 0.7526), in MDC 08 (Diseases and Disorders of the Musculoskeletal System and Connective Tissue), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
It was added in FY2026, effective October 1, 2025.
Coding notes
Notes that apply from higher levels
Instructions written at a parent level also apply to M05.A.
Broader instructions also apply from Chapter 13: Diseases of the musculoskeletal system and connective tissue.
Alphabetic index entries
1 entriesTerms in the official ICD-10-CM index that lead to M05.A.
MS-DRG v44.0 grouping
All DRGs →Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.
MDC 08 · Diseases and Disorders of the Musculoskeletal System and Connective Tissue
Code history
- 2016
- 2017
- 2018
- 2019
- 2020
- 2021
- 2022
- 2023
- 2024
- 2025
- 2026
- 2027
- FY2026 (effective 10/1/2025): Added
- No changes since FY2026.
Common questions about M05.A
Is M05.A billable?
- Yes. M05.A is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can M05.A be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict M05.A as a principal diagnosis.
Is M05.A a CC or MCC?
- No. M05.A is neither a CC nor an MCC under MS-DRG v44.0.
What DRG does M05.A group to?
- M05.A is used in the MS-DRG v44.0 logic for MS-DRG 545 (Connective Tissue Disorders with MCC), MS-DRG 546 (Connective Tissue Disorders with CC) and MS-DRG 547 (Connective Tissue Disorders without CC/MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.