2026 ICD-10-CM Diagnosis Code J11.81Influenza due to unidentified influenza virus with encephalopathy
ICD-10-CM Codes›J00–J99›J09-J18›J11
- Billable — Valid for Submission
- Not Chronic
J11.81 is a billable ICD-10-CM diagnosis code for influenza due to unidentified influenza virus with encephalopathy. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 865 through 866. Coders also document this condition as encephalitis caused by influenza virus. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Influenza and Other nervous system disorders (neither hereditary nor degenerative).
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Encephalitis caused by influenza virus
- Influenza with encephalopathy
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Influenzal encephalopathy NOS
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
External Cause of Injuries IndexGuidance
References for this code in the External Cause of Injuries Index.
- Influenza(bronchial) (epidemic) (respiratory (upper)) (unidentified influenza virus)
- with
- encephalopathy
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Flu
The flu, also called influenza, is a respiratory infection caused by viruses. Each year, millions of Americans get sick with the flu. Sometimes it causes mild illness. But it can also be serious or even deadly, especially for people over 65, newborn babies, and people with certain chronic illnesses.
The full article covers:
- What is the flu?
- What causes the flu?
- What are the symptoms of the flu?
- What other problems can the flu cause?
- How is the flu diagnosed?
- What are the treatments for the flu?
- Can the flu be prevented?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert J11.81 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About J11.81Overview
Is J11.81 a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report influenza due to unidentified influenza virus with encephalopathy on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does J11.81 group to?
When influenza due to unidentified influenza virus with encephalopathy is the principal diagnosis on an inpatient stay, it groups to MS-DRG 865, 866, with relative weights from 0.8696 to 1.4983 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of J11.81?
Under the General Equivalence Mappings, influenza due to unidentified influenza virus with encephalopathy converts to ICD-9-CM 487.8 (flu w manifestation NEC). The mapping is approximate, so confirm the match fits the documentation.
Footnotes
[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.
