Excludes1 pair

A42.0 vs J17

A42.0 and J17 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 J17
pneumonia in actinomycosis (A42.0)
A42.0

Pulmonary actinomycosis

Billable
Chapter 1
Certain infectious and parasitic diseases
Section
A30-A49
Indexed under
  • Actinomycosis, actinomycotic › with pneumonia
  • Actinomycosis, actinomycotic › pulmonary
  • Pneumonia › in › actinomycosis
J17

Pneumonia in diseases classified elsewhere

Billable
Chapter 10
Diseases of the respiratory system
Section
J09-J18
Indexed under
  • Pneumonia › postinfectional NEC
  • Pneumonia › rheumatic
  • Rheumatic › pneumonia
  • Bilharziasis › pulmonary NOS › pneumonia
  • Pneumonia › in › rheumatic fever

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