ICD-10 Code J11.81 – Influenza due to unidentified influenza virus with encephalopathy (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code J11.81 – Influenza due to unidentified influenza virus with encephalopathy
What it is
J11.81 identifies influenza caused by an unidentified influenza virus when encephalopathy is present. Use it when the record links influenza to brain dysfunction, but the virus type is not specified.
Clinical signs
Clinical features vary; refer to documentation. Encephalopathy may appear as altered mental status, confusion, reduced alertness, or other neurologic dysfunction occurring with influenza.
When to use this code
Use this code when the provider documents influenza and encephalopathy together, and the influenza virus is not identified as type A or B. The record should support a causal relationship or clearly associate the encephalopathy with the flu. Check documentation if the neurologic finding is not clearly linked to influenza.
Do not use for
Do not use J11.81 when the influenza virus is identified, or when encephalopathy is due to another cause. Do not apply it for uncomplicated influenza without neurologic involvement.
Coding tip
Verify that the chart supports both influenza and encephalopathy, and code the unspecified virus only when no specific influenza type is documented.