B59 vs J16
B59 and J16 can never be reported together. ICD-10-CM declares them mutually exclusive with an Excludes1 note, meaning the two conditions cannot occur in the same patient — so exactly one of them is correct for any given encounter.
The official note, declared on J16
pneumocystosis (B59)
B59
Pneumocystosis
Billable
- Chapter 1
- Certain infectious and parasitic diseases
- Section
- B50-B64
Use when the record says
- Pneumonia due to Pneumocystis carinii
- Pneumonia due to Pneumocystis jirovecii
Indexed under
- Pneumocystis carinii pneumonia
- Pneumocystis jirovecii (pneumonia)
- Pneumocystosis (with pneumonia)
- Infection, infected, infective › Pneumocystis carinii (opportunistic)
- Infection, infected, infective › Pneumocystis jirovecii (opportunistic)
J16
Pneumonia due to other infectious organisms, not elsewhere classified
Not billable
- Chapter 10
- Diseases of the respiratory system
- Section
- J09-J18
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