FY2027
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Excludes1 pair

I77.6 vs M31.6

I77.6 and M31.6 are not coded together. ICD-10-CM declares them mutually exclusive with an Excludes1 note — the two conditions are not expected to occur together, so exactly one of them is normally correct for a given encounter. The Official Guidelines carve out one exception: if the two conditions are clearly unrelated to each other, both may be reported.

The official note, declared on I77.6
giant cell (M31.5, M31.6)
I77.6

Arteritis, unspecified

BillableUnspecified
Chapter 9
Diseases of the circulatory system
Section
I70-I79
Use when the record says
  • Aortitis NOS
  • Endarteritis NOS
Indexed under
  • Angiitis
  • Aortitis (nonsyphilitic) (calcific)
  • Arteriolitis
  • Arteritis
  • Endarteritis (bacterial, subacute) (infective)
M31.6

Other giant cell arteritis

Billable
Chapter 13
Diseases of the musculoskeletal system and connective tissue
Section
M30-M36
Indexed under
  • Arteritis › cranial, giant cell (left) (right)
  • Arteritis › giant cell NEC
  • Arteritis › temporal, giant cell
  • Myopathy › in › giant cell arteritis

These two codes sit in different chapters of the Tabular List, which is usually the clearest signal that they describe different underlying processes rather than different degrees of the same one.

Excludes1 is not always absolute: where two conditions covered by the note are genuinely unrelated, CMS guidance permits reporting both. Document the reasoning rather than assuming it. More on Excludes1 vs Excludes2 · FY2027