M05.A: Abnormal rheumatoid factor and anti-citrullinated protein antibody with rheumatoid arthritis

New code · FY2026

Billable: use this code on claims.

• New code, effective October 1, 2025 (FY2026).

Code breakdown

Coding notes

Code first

• rheumatoid arthritis with rheumatoid factor by site, if known (M05.00 to M05.8A)

Excludes1 (from M05)

• rheumatic fever (I00)
• juvenile rheumatoid arthritis (M08.-)
• rheumatoid arthritis of spine (M45.-)

Medicare coverage

M05.A is listed as a covered diagnosis in 2 Medicare billing and coding articles:

• A56380 Billing and Coding: Rituximab
• A56432 Billing and Coding: Infliximab

Check this code

• Code search: full entry and nearby codes
• Excludes checker: can it be billed with another code?
• Coverage checker: is it covered for your CPT code?

All FY2026 ICD-10-CM changes

ICD-10-CM codes and descriptions are from the CMS and NCHS code files. Coverage is from the CMS Medicare Coverage Database billing and coding articles.