2026 ICD-10-CM Diagnosis Code I33Acute and subacute endocarditis

ICD-10-CM Codes›I00–I99›I30-I5A›I33

ICD-10-CM I33
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

I33 is a non-billable ICD-10-CM category code for acute and subacute endocarditis, so it cannot be submitted on claims. Use a more specific code from this category instead, such as I33.0 and I33.9.

Code Identity

ICD-10-CM Code
I33
Billable Status
No — Non-Billable Category
Code Describes
Acute and subacute endocarditis
Chapter
I30-I5A
Other forms of heart disease

Code Classification

ChapterI00–I99Diseases of the circulatory system
SectionI30-I5AOther forms of heart disease
CategoryI33Acute and subacute endocarditis
This CodeI33Acute and subacute endocarditis

Specific Coding for Acute and subacute endocarditisOverview

Non-specific codes like I33 require more characters. Use one of these billable codes instead:

  • Use I33.0 for Acute and subacute infective endocarditis

  • Use I33.9 for Acute and subacute endocarditis, unspecified

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Type 1 Excludes

  • acute rheumatic endocarditis I01.1
  • endocarditis NOS I38

Patient EducationClinical

Endocarditis

Endocarditis is sometimes called infective endocarditis. It's a rare but life-threatening inflammation of the lining inside your heart's chambers and valves (the endocardium).

The full article covers:

  • What is endocarditis?
  • What causes endocarditis?
  • Who is more likely to develop endocarditis?
  • What are the symptoms of endocarditis?
  • What other problems can endocarditis cause?
  • How is endocarditis diagnosed?
  • What are the treatments for endocarditis?
  • Can endocarditis be prevented?

Read the full article at MedlinePlus

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

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 I33Overview

Is I33 (Acute and subacute endocarditis) a billable code?

No. This is a category header that groups the codes for acute and subacute endocarditis, and headers cannot be submitted on claims. Claims for acute and subacute endocarditis need a more specific code from this category, such as I33.0 and I33.9.