Excludes1 pair
A85- vs B26.2
A85 and B26.2 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 A85
encephalitis due to mumps virus (B26.2)
A85
Other viral encephalitis, not elsewhere classified
Not billable
- Chapter 1
- Certain infectious and parasitic diseases
- Section
- A80-A89
Use when the record says
- specified viral encephalomyelitis NEC
- specified viral meningoencephalitis NEC
B26.2
Mumps encephalitis
Billable
- Chapter 1
- Certain infectious and parasitic diseases
- Section
- B25-B34
Indexed under
- Meningoencephalitis › mumps
- Mumps › encephalitis
- Mumps › meningoencephalitis
- Encephalitis › in › mumps
- Meningoencephalitis › in › mumps
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