ICD-10 I33.9
Billable / Specific MCCAcute and subacute endocarditis, unspecified
About ICD-10-CM I33.9
ICD-10-CM code I33.9 represents Acute and subacute endocarditis, unspecified. This is a billable/specific code in the Circulatory System chapter (block I33). The 2026 edition of ICD-10-CM I33.9 became effective on October 1, 2025.
Coding Tips for I33.9
Specialist guidance from the PayerReady Medical Coding Team. Specificity warnings, HCC capture rules, sequencing notes.
I33.9 is designated MCC for MS-DRG grouping. On inpatient claims, this code can shift the DRG to the with-MCC variant when documented as a present-on-admission secondary diagnosis. Hospital CDI programs flag MCC opportunities during chart review. Failure to capture this code may leave 30 to 80 percent of the inpatient stay revenue unrealized.
Inclusion Terms / Approximate Synonyms
Clinical terms and conditions classified under I33.9. Per CMS ICD-10-CM Tabular 2026.
- Acute endocarditis NOS
- Acute myoendocarditis NOS
- Acute periendocarditis NOS
- Subacute endocarditis NOS
- Subacute myoendocarditis NOS
- Subacute periendocarditis NOS
Inpatient DRG Impact, MCC
codes Acute and subacute endocarditis, unspecified. As a Major Complication/Comorbidity (MCC), this can shift the DRG assignment to a higher-weighted category, substantial reimbursement impact.
Medicare LCD Coverage for I33.9
Local Coverage Determinations (LCDs) from CMS MACs that list I33.9 as a covered diagnosis.
Showing top 10 of 263 total . Click a CPT for full coverage scope.
Commercial Payer Coverage
Coverage policies from major commercial payers referencing I33.9.
2 Aetna
1 Cigna
5 Medicare
CPT Codes Commonly Billed with I33.9
Procedures frequently paired with this diagnosis based on PayerReady's Dx↔Px linkage data.
We don't have CPT pairings indexed for this specific code yet. Use the CPT search above to find common procedures, or check your payer's published medical policy for code-specific guidance.
Convert I33.9 to ICD-9-CM
Per CMS General Equivalence Mappings (GEMs), useful for legacy data review and historical claim analysis.
| ICD-10 | ICD-9 | Mapping Flags |
|---|---|---|
| I33.9 | 4219 | 00000 |
Flags format (5 digits): Approximate · No Map · Combination · Scenario · Choice List. Source: CMS 2017 GEMs (final version).
Codes Adjacent To I33.9
Other codes in section I30-I5A (Other forms of heart disease).
ICD-10 I33.9, Billing FAQ
Is ICD-10 code I33.9 billable? +
Yes, I33.9 is a billable ICD-10-CM code that can appear as a primary or secondary diagnosis on claims.
What other names or terms map to I33.9? +
ICD-10 I33.9 includes: Acute endocarditis NOS; Acute myoendocarditis NOS; Acute periendocarditis NOS, and 3 more clinical synonyms.
Is I33.9 a CC or MCC for inpatient DRG? +
Yes, this code is designated as MCC. Documenting as a secondary diagnosis on inpatient claims can shift the DRG to a higher-weighted category.
What ICD-9 codes does I33.9 map to? +
Per CMS GEMs, I33.9 maps to ICD-9 codes: 4219. Useful for legacy data review and historical claim analysis.
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Reviewed by the PayerReady Medical Coding Team
Verified against the CMS 2026 code set on May 31, 2026.
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