2027 ICD-10-CM Diagnosis Code A85.1Adenoviral encephalitis
ICD-10-CM Codes›A00–B99›A80-A89›A85
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Not Chronic
A85.1 is a billable ICD-10-CM diagnosis code for adenoviral encephalitis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 97 through 99, 974 through 976. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 188 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis and Viral infection.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Acute adenoviral encephalitis
- Acute adenoviral meningoencephalitis
- Acute encephalitis
- Acute meningitis
- Acute viral encephalitis
- Adenoviral encephalitis
- Adenoviral meningitis
- Adenoviral nervous system infection
- Encephalitis with AIDS
- Encephalopathy with AIDS
- Meningoencephalitis caused by virus
- Subacute adenoviral encephalitis
- Subacute adenoviral encephalitis co-occurrent with human immunodeficiency virus infection
- Subacute adenoviral encephalitis with AIDS
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to A85.1: its own notes plus those printed at A85, block A80-A89, and Chapter 1. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- specified viral encephalomyelitis NEC
- specified viral meningoencephalitis NEC
- diseases generally recognized as communicable or transmissible
Applicable To
Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.
- Adenoviral meningoencephalitis
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- encephalitis due to cytomegalovirus (B25.8)
- encephalitis due to herpesvirus NEC (B10.0-)
- encephalitis due to herpesvirus [herpes simplex] (B00.4)
- encephalitis due to measles virus (B05.0)
- encephalitis due to mumps virus (B26.2)
- encephalitis due to poliomyelitis virus (A80.-)
- encephalitis due to zoster (B02.0)
- lymphocytic choriomeningitis (A87.2)
- myalgic encephalomyelitis (G93.32)
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may 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)
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify resistance to antimicrobial drugs (Z16.-)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name A85.1, its category, or a range that includes it.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Encephalitis
Encephalitis is inflammation (swelling) of the brain. It can happen when an infection or medical condition that affects the brain activates your immune system. The inflammation can cause a wide range of symptoms. In extreme cases, it can lead to brain damage, stroke, or even death.
The full article covers:
- What is encephalitis?
- What causes encephalitis?
- Who is more likely to get encephalitis?
- What are the symptoms of encephalitis?
- How is encephalitis diagnosed?
- What are the treatments for encephalitis?
- Can encephalitis be prevented?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert A85.1 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About A85.1Overview
What is the ICD-10 code for adenoviral encephalitis?
The ICD-10-CM code for adenoviral encephalitis is A85.1 (sometimes written as A851). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is A85.1 (Other viral encephalitis, not elsewhere classified) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report adenoviral encephalitis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does A85.1 group to?
When adenoviral encephalitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 98, 974, 976, 99, 975, 97, with relative weights from 0.7879 to 3.8208 depending on complications. Higher weights mean higher Medicare reimbursement.
Is A85.1 a CC or MCC?
CMS lists A85.1 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 188 closely related codes in its exclusion list.
Can A85.1 be reported with B25.8?
Not as a rule. The Excludes1 note at A85, which applies to A85.1, lists "encephalitis due to cytomegalovirus (B25.8)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
