2026 ICD-10-CM Diagnosis Code B27.00Gammaherpesviral mononucleosis without complication

ICD-10-CM Codes›A00–B99›B25-B34›B27

ICD-10-CM B27.00
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

B27.00 is a billable ICD-10-CM diagnosis code for gammaherpesviral mononucleosis without complication. 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 chronic active Epstein-Barr virus infection of T- and NK-cell type infection systemic form. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Viral infection.

Code Identity

ICD-10-CM Code
B27.00
Billable Status
Yes — Valid for Submission
Code Describes
Gammaherpesviral mononucleosis without complication
Short Description
Gammaherpesviral mononucleosis without complication
Same as the full description in the CMS dataset.
Parent Code
B27.0
Gammaherpesviral mononucleosis

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB25-B34Other viral diseases
CategoryB27Infectious mononucleosis
This CodeB27.00Gammaherpesviral mononucleosis without complication

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Chronic active Epstein-Barr virus infection of T- and NK-cell type infection systemic form
  • Chronic Epstein-Barr virus infection syndrome
  • Epstein Barr virus infection of the central nervous system
  • Epstein-Barr virus disease
  • Epstein-Barr virus infectious mononucleosis
  • Gammaherpesviral mononucleosis
  • Glandular fever pharyngitis

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.

    • Mononucleosis, infectious
      • Epstein-Barr (virus)
    • Mononucleosis, infectious
      • gammaherpesviral

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

Infectious Mononucleosis

Infectious mononucleosis (mono) is a disease caused by viruses.The most common cause is the Epstein-Barr virus (EBV). Mono is contagious, which means it can spread from person to person. It is common among teenagers and young adults, especially college students.

The full article covers:

  • What is infectious mononucleosis (mono)?
  • What causes infectious mononucleosis (mono)?
  • What are the symptoms of infectious mononucleosis (mono)?
  • How is infectious mononucleosis (mono) diagnosed?
  • What are the treatments for infectious mononucleosis (mono)?
  • Can infectious mononucleosis (mono) be prevented?

Read the full article at MedlinePlus

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

Convert B27.00 to ICD-9-CMHistory

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

ICD-9-CM
075 Infectious mononucleosis
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About B27.00Overview

Is B27.00 (Gammaherpesviral mononucleosis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report gammaherpesviral mononucleosis without complication on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does B27.00 group to?

When gammaherpesviral mononucleosis without complication 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 B27.00?

Under the General Equivalence Mappings, gammaherpesviral mononucleosis without complication converts to ICD-9-CM 075 (infectious mononucleosis). 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.