2027 ICD-10-CM Diagnosis Code I33.9Acute and subacute endocarditis, unspecified
ICD-10-CM Codes›I00–I99›I30-I5A›I33
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- Chronic Condition
I33.9 is a billable ICD-10-CM diagnosis code for acute and subacute endocarditis, unspecified. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 288 through 290, 791, 793, 974 through 976. 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 15 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Endocarditis and endocardial disease.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Abscess at site of interatrial communication
- Abscess at site of ventricular septal defect
- Abscess of cardiac septum
- Acute endocarditis
- Acute endocarditis co-occurrent with human immunodeficiency virus infection
- Acute myoendocarditis
- Acute nonbacterial endocarditis
- Acute periendocarditis
- Embolism due to non-infective heart valve vegetations
- Heart disease co-occurrent with human immunodeficiency virus infection
- Subacute endocarditis
- Subacute myoendocarditis
- Subacute pericarditis
- Subacute periendocarditis
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to I33.9: its own notes plus those printed at I33 and Chapter 9. A note printed at a category, block or chapter applies to every code under it.
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.
- Acute endocarditis NOS
- Acute myoendocarditis NOS
- Acute periendocarditis NOS
- Subacute endocarditis NOS
- Subacute myoendocarditis NOS
- Subacute periendocarditis NOS
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
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.
- certain conditions originating in the perinatal period (P04-P96)
- certain infectious and parasitic diseases (A00-B99)
- complications of pregnancy, childbirth and the puerperium (O00-O9A)
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
- endocrine, nutritional and metabolic diseases (E00-E88)
- injury, poisoning and certain other consequences of external causes (S00-T88)
- neoplasms (C00-D49)
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
- systemic connective tissue disorders (M30-M36)
- transient cerebral ischemic attacks and related syndromes (G45.-)
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.
Endocarditis (chronic) (marantic) (nonbacterial) (thrombotic) (valvular) I38
acute or subacute I33.9
aortic (heart) (nonrheumatic) (valve) I35.8
acute or subacute I33.9
mitral (chronic) (double) (fibroid) (heart) (inactive) (valve) (with chorea) I05.9
pulmonary (chronic) (heart) (valve) I37.8
acute or subacute I33.9
toxic I33.9
tricuspid (chronic) (heart) (inactive) (rheumatic) (valve) (with chorea) I07.9
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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.
Convert I33.9 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About I33.9Overview
What is the ICD-10 code for acute and subacute endocarditis, unspecified?
The ICD-10-CM code for acute and subacute endocarditis, unspecified is I33.9 (sometimes written as I339). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is I33.9 (Acute and subacute endocarditis) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report acute and subacute endocarditis, unspecified on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does I33.9 group to?
When acute and subacute endocarditis, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 289, 791, 974, 976, 975, 288, 290, with relative weights from 0.7843 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.
Is I33.9 a CC or MCC?
CMS lists I33.9 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 15 closely related codes in its exclusion list.
Can I33.9 be reported with I01.1?
Not as a rule. The Excludes1 note at I33, which applies to I33.9, lists "acute rheumatic endocarditis (I01.1)". 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).
