ICD-10 Code A85.1 – Adenoviral encephalitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A85.1 – Adenoviral encephalitis
What it is
A85.1 identifies encephalitis caused by adenovirus. Use it when the record documents adenoviral infection with inflammation of the brain.
Clinical signs
Clinical features vary; refer to documentation. Encephalitis may present with fever, headache, altered mental status, seizures, or focal neurologic findings, but the adenoviral cause must be documented or clearly established.
When to use this code
Use A85.1 when the provider states adenoviral encephalitis, adenovirus-related encephalitis, or a confirmed adenoviral central nervous system infection. It may also apply when the final diagnosis links encephalitis to adenovirus in the chart. If the cause is not specified, check documentation before coding.
Do not use for
Do not use this code for adenoviral upper respiratory, gastrointestinal, or eye infections without encephalitis. Do not assign it for unspecified viral encephalitis unless adenovirus is documented.
Coding tip
Code the confirmed cause only when the provider documents adenovirus as the etiology; otherwise, query or use the unspecified encephalitis code set.