2027 ICD-10-CM Diagnosis Code B33.21Viral endocarditis

ICD-10-CM Codes›A00–B99›B25-B34›B33

ICD-10-CM B33.21
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

B33.21 is a billable ICD-10-CM diagnosis code for viral endocarditis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 306 through 307. 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 86 closely related codes. Coders also document this condition as coxsackie carditis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Endocarditis and endocardial disease and Viral infection.

Code Identity

ICD-10-CM Code
B33.21
Billable Status
Yes — Valid for Submission
Code Describes
Viral endocarditis
Short Description
Viral endocarditis
Same as the full description in the CMS dataset.
Parent Code
B33.2
Viral carditis

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB25-B34Other viral diseases
CategoryB33Other viral diseases, not elsewhere classified
This CodeB33.21Viral endocarditis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Coxsackie carditis
  • Coxsackie endocarditis
  • Enterovirus heart infection
  • Viral endocarditis

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to B33.21: its own notes plus those printed at 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

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.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name B33.21, its category, or a range that includes it.

Applicable To 1

These notes mention B33.21.

  • O98.5 Other viral diseases complicating pregnancy, childbirth and the puerperium
    Conditions in A80-B09, B25-B34, R87.81-, R87.82- names B25-B34, which includes this code

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 CIR004
Endocarditis and endocardial disease
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR INF008
Viral infection
Default principal diagnosis: inpatient No · outpatient No

Clinical InformationClinical

  • Viral Endocarditis

    endocarditis caused by a viral infection.

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 B33.21 to ICD-9-CMHistory

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

ICD-9-CM
074.22 Coxsackie endocarditis
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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About B33.21Overview

What is the ICD-10 code for viral endocarditis?

The ICD-10-CM code for viral endocarditis is B33.21 (sometimes written as B3321). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is B33.21 (Viral carditis) a billable code?

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

What MS-DRG does B33.21 group to?

When viral endocarditis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 306, 307, with relative weights from 0.9146 to 1.5457 depending on complications. Higher weights mean higher Medicare reimbursement.

Is B33.21 a CC or MCC?

CMS lists B33.21 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 86 closely related codes in its exclusion list.

What is the ICD-9 equivalent of B33.21?

Under the General Equivalence Mappings, viral endocarditis converts to ICD-9-CM 074.22 (coxsackie endocarditis). The mapping is approximate, so confirm the match fits the documentation.