2027 ICD-10-CM Diagnosis Code A84.89Other tick-borne viral encephalitis

ICD-10-CM Codes›A00–B99›A80-A89›A84

ICD-10-CM A84.89
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

A84.89 is a billable ICD-10-CM diagnosis code for other tick-borne viral encephalitis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 23 through 24, 97 through 99. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 36 closely related codes. Coders also document this condition as encephalitis caused by Siberian tick-borne encephalitis virus. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis and Viral infection.

Code Identity

ICD-10-CM Code
A84.89
Billable Status
Yes — Valid for Submission
Code Describes
Other tick-borne viral encephalitis
Short Description
Other tick-borne viral encephalitis
Same as the full description in the CMS dataset.
Parent Code
A84.8
Other tick-borne viral encephalitis

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA80-A89Viral and prion infections of the central nervous system
CategoryA84Tick-borne viral encephalitis
This CodeA84.89Other tick-borne viral encephalitis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Encephalitis caused by Siberian tick-borne encephalitis virus
  • Encephalitis caused by tick-borne encephalitis virus
  • Louping ill virus encephalitis

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to A84.89: its own notes plus those printed at A84, 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.

From A84 Tick-borne viral encephalitis applies to 5 codes
  • tick-borne viral meningoencephalitis
From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • 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.

  • Louping ill

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From Block A80-A89 Viral and prion infections of the central nervous system applies to 48 codes
  • postpolio syndrome (G14)
  • sequelae of poliomyelitis (B91)
  • sequelae of viral encephalitis (B94.1)

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.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • 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)

Code First

The underlying condition named in the note is sequenced before this code.

  • if applicable, transfusion related infection (T80.22-)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • code to identify resistance to antimicrobial drugs (Z16.-)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

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.

CCSR NVS002
Encephalitis
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR INF008
Viral infection
Default principal diagnosis: inpatient No · outpatient No

Clinical InformationClinical

  • Louping Ill

    an acute tick-borne arbovirus infection causing meningoencephalomyelitis of sheep.

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.

Code History & ChangesHistory

Replacement A84.89 replaces the following previously assigned code(s):

  • A84.8 - Other tick-borne viral encephalitis
FY 2021AddedAdded to the ICD-10-CM code setEffective October 1, 2020.
FY 2022–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About A84.89Overview

What is the ICD-10 code for other tick-borne viral encephalitis?

The ICD-10-CM code for other tick-borne viral encephalitis is A84.89 (sometimes written as A8489). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is A84.89 (Other tick-borne viral encephalitis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other tick-borne viral encephalitis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does A84.89 group to?

When other tick-borne viral encephalitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 24, 98, 99, 23, 97, with relative weights from 1.5249 to 5.7422 depending on complications. Higher weights mean higher Medicare reimbursement.

Is A84.89 a CC or MCC?

CMS lists A84.89 as an MCC (major complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 36 closely related codes in its exclusion list.

Can A84.89 be reported with G14?

Not as a rule. The Excludes1 note at block A80-A89, which applies to A84.89, lists "postpolio syndrome (G14)". 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).