A86 — Unspecified viral encephalitis
Is A86 billable?
Yes, but A86 is an unspecified code. A86 is a valid, billable ICD-10-CM code for encounters from October 1, 2026 through September 30, 2027. However, A86 is an unspecified or catch-all code. Payers apply additional scrutiny to unspecified codes and many deny them when the medical record supports a more specific option, so check the documentation before selecting A86.
A86 at a glance
| Code | A86 |
|---|---|
| Description | Unspecified viral encephalitis |
| Billable | Yes |
| Code set | ICD-10-CM FY2027 |
| Valid for encounters | October 1, 2026 – September 30, 2027 |
Which MS-DRGs does A86 group to?
A86 sits in MDC 01 and helps define the logic of 3 MS-DRGs (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.
- 097Non-Bacterial Infection of Nervous System Except Viral Meningitis with MCCmedical
- 098Non-Bacterial Infection of Nervous System Except Viral Meningitis with CCmedical
- 099Non-Bacterial Infection of Nervous System Except Viral Meningitis without CC/MCCmedical
As a secondary diagnosis, A86 is a complication or comorbidity (CC), which can move a stay into a higher-paying DRG.
How is A86 listed in the Alphabetic Index?
These are the routes through the Alphabetic Index that lead to A86. They show the wording a clinician may have documented, which often differs from the Tabular description.
- Encephalitis › acute (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
- Encephalitis › endemic (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
- Encephalitis › epidemic NEC (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
- Encephalitis › infectiousNEC (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
- Encephalitis › postviral NEC (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
- Encephalitis › viral, virus (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
- Meningoencephalitis › acute NEC
- Meningoencephalitis › infectious
- Meningoencephalitis › virus NEC
- Meningoencephalomyelitis › acute NEC
Inclusion terms
Alternative wording in documentation that is classified to A86.
- Viral encephalomyelitis NOS
- Viral meningoencephalitis NOS
Excludes1 — never code together — inherited from A80-A89
The conditions below can never be reported together with A86 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.
Use additional code — inherited from Chapter 1
Report an additional code alongside A86 to fully describe the condition. A86 is sequenced first.
- code to identify resistance to antimicrobial drugs (Z16.-)
Excludes2 — not included here — inherited from Chapter 1
The conditions below are not part of A86, but a patient may have both at the same time. When documentation supports it, A86 and the excluded code may both be reported.
- carrier or suspected carrier of infectious disease (Z22.-)
- certain localized infections - see body system-related chapters
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
- infectious and parasitic diseases specific to the perinatal period (P35-P39)
- influenza and other acute respiratory infections (J00-J22)
How long has A86 existed?
A86 has been in ICD-10-CM since at least FY2016, the earliest fiscal year on record here.
Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.
Which codes are confused with A86?
ICD-10-CM declares these codes mutually exclusive with A86 — exactly one of each pair can be correct for a given encounter.