2027 ICD-10-CM Diagnosis Code B08.21Exanthema subitum [sixth disease] due to human herpesvirus 6

ICD-10-CM Codes›A00–B99›B00-B09›B08

ICD-10-CM B08.21
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

B08.21 is a billable ICD-10-CM diagnosis code for exanthema subitum [sixth disease] due to human herpesvirus 6. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 791, 793, 865 through 866. The code is restricted by the Medicare Code Editor to pediatric patients (age 0 through 17). Coders also document this condition as exanthema subitum. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Viral infection.

Code Identity

ICD-10-CM Code
B08.21
Billable Status
Yes — Valid for Submission
Code Describes
Exanthema subitum [sixth disease] due to human herpesvirus 6
Short Description
Exanthema subitum [sixth disease] due to human herpesvirus 6
Same as the full description in the CMS dataset.
Parent Code
B08.2
Exanthema subitum [sixth disease]

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB00-B09Viral infections characterized by skin and mucous membrane lesions
CategoryB08Other viral infections characterized by skin and mucous membrane lesions, not elsewhere classified
This CodeB08.21Exanthema subitum [sixth disease] due to human herpesvirus 6

Code EditsBilling

Medicare Code Editor checks that affect claim validity for B08.21.

Pediatric diagnoses
The Medicare Code Editor detects inconsistencies in pediatric cases by checking a patient's age and any diagnosis on the patient's record. The pediatric code edits apply to patients age range is 0–17 years inclusive (e.g., Reye's syndrome, routine child health exam).

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Exanthema subitum
  • Human herpes virus 6 infection of skin
  • Infection by human herpesvirus 6
  • Infection caused by Roseolovirus
  • Roseola infantum caused by human herpesvirus 6

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to B08.21: its own notes plus those printed at B08 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 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.

  • Roseola infantum due to human herpesvirus 6

Excludes1

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

From B08 Other viral infections characterized by skin and mucous membrane lesions, not elsewhere classified applies to 22 codes
  • vesicular stomatitis virus disease (A93.8)

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)

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 INF008
Viral infection
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Viral Infections

Viruses are very tiny germs. They are made of genetic material (either DNA or RNA) inside of a protein coating. There are a huge number of viruses on earth. Only a small number of them can infect humans. Those viruses can infect our cells, which may cause disease.

The full article covers:

  • What are viruses?
  • How are viruses spread?
  • How do viruses cause disease?
  • What are the treatments for viral infections?
  • Can viral infections be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert B08.21 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
058.11 Roseola infant d/t HHV-6
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About B08.21Overview

What is the ICD-10 code for exanthema subitum [sixth disease] due to human herpesvirus 6?

The ICD-10-CM code for exanthema subitum [sixth disease] due to human herpesvirus 6 is B08.21 (sometimes written as B0821). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is B08.21 (Exanthema subitum [sixth disease]) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report exanthema subitum [sixth disease] due to human herpesvirus 6 on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does B08.21 group to?

When exanthema subitum [sixth disease] due to human herpesvirus 6 is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 791, 866, 865, with relative weights from 0.8691 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.

Who can B08.21 be reported for?

The Medicare Code Editor checks exanthema subitum [sixth disease] due to human herpesvirus 6 against patient demographics: this code is intended for pediatric patients (age 0 through 17). Claims outside these limits are flagged as inconsistent.

Can B08.21 be reported with A93.8?

Not as a rule. The Excludes1 note at B08, which applies to B08.21, lists "vesicular stomatitis virus disease (A93.8)". 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).