A86 ICD-10-CM Code: Unspecified viral encephalitis
HCC Buddy Code Card
Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.
FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Viral and prion infections of the central nervous system (A80-A89)
A86
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceUnspecified viral encephalitis
This code describes inflammation of the brain caused by a virus when the specific virus has not been identified or documented. It's used when a patient has symptoms of viral brain inflammation but testing hasn't determined which virus is responsible.
CMS-HCC V28
N/A—
Not mapped
CMS-HCC V24
N/A—
Not mapped
ACA/HHS
MappedHCC 3
Varies by metal level
ESRD/PACE
N/A—
Not mapped
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
Official- Viral encephalomyelitis NOS
- Viral meningoencephalitis NOS
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for A86 in this effective period.
Related Child Codes
ICD-10-CM does not list child codes under A86 for this display context.
Includes
OfficialICD-10-CM does not list Includes notes for A86 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for A86 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for A86 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for A86 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for A86 in this effective period.
Buddy Documentation Tip
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is A86 an HCC code?
No. A86 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
Coder workflow notes
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This code does not map to an HCC category in any model (V28, V24, ESRD, RxHCC).
What This Code Means
A86 is the ICD-10-CM diagnosis code for unspecified viral encephalitis. This code describes inflammation of the brain caused by a virus when the specific virus has not been identified or documented. It's used when a patient has symptoms of viral brain inflammation but testing hasn't determined which virus is responsible. A86 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering viral and prion infections of the central nervous system (a80-a89).
A86 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.
Use this code only when the specific viral cause cannot be determined; if the virus is identified (such as HSV, West Nile, or enterovirus), use the more specific code instead.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A86 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code only when the specific viral cause cannot be determined; if the virus is identified (such as HSV, West Nile, or enterovirus), use the more specific code instead
- •Ensure documentation supports encephalitis diagnosis (not just meningitis or other CNS conditions) and that viral etiology is confirmed or strongly suspected before coding