Excludes1 pair
A85- vs B00.4
A85 and B00.4 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 herpesvirus [herpes simplex] (B00.4)
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
B00.4
Herpesviral encephalitis
Billable
- Chapter 1
- Certain infectious and parasitic diseases
- Section
- B00-B09
Use when the record says
- Herpesviral meningoencephalitis
- Simian B disease
Indexed under
- Disease, diseased › simian B
- Encephalitis › herpesviral
- Herpes, herpesvirus, herpetic › encephalitis
- Meningoencephalitis › herpesviral, herpetic
- Encephalitis › in › herpes virus (simplex)
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