ICD-10 Code I38: Endocarditis, Valve Unspecified

ICD-10 code I38 is a billable ICD-10-CM diagnosis code for endocarditis, valve unspecified, valid for use in FY2026 medical claims and HIPAA-covered electronic transactions. It applies when the clinical documentation confirms endocarditis or valvular heart disease. The record must still lack the specificity for a more precise code, whether by valve site or causative organism.

This lack of specificity is exactly where claims go wrong. Coders who reach for I38 without ruling out a more specific diagnosis first, such as I33.0 or I09.1, risk both under-coding and denial. I38’s Excludes1 note is a hard stop for the conditions it lists: congenital valve defects, endocardial fibroelastosis, and rheumatic disease.

This reference covers code details, includes and excludes notes, synonyms, and related codes. It also covers I38 vs I33 and I38 vs I39 comparisons, documentation requirements, and billing guidance for FY2026.

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Key takeaways

ICD-10 code I38 covers chronic endocarditis NOS and unspecified valve dysfunction, such as incompetence or stenosis, with no valve, organism, or cause named.

I38’s Excludes1 note covers congenital valve insufficiency or stenosis NOS (Q24.8), endocardial fibroelastosis (I42.4), and rheumatic endocarditis (I09.1). I33 and I39 sit outside that list; a coder rules them out by judgment, not by a formal exclusion.

I39 (endocarditis in diseases classified elsewhere) is a manifestation code used only when an underlying disease such as Q fever is documented and coded first.

Pabau, practice management software with integrated billing, connects to Claim.MD to catch missing documentation before it forces coders into an unspecified code.

ICD-10 code I38: Definition, billable status, and FY2026 effective date

ICD-10 code I38 is the American ICD-10-CM code for endocarditis, valve unspecified. It sits within the I30-I5A block (Other forms of heart disease) under the broader I00-I99 circulatory system chapter. The code became effective on October 1, 2025 for the FY2026 coding year.

According to the Centers for Medicare and Medicaid Services (CMS), I38 is a billable, specific diagnosis code valid for claim submission in HIPAA-covered electronic transactions. It has no child codes; it is a terminal leaf in the ICD-10-CM hierarchy.

Understanding where I38 sits in the revenue cycle management workflow matters. Its NOS (not otherwise specified) status puts it at the boundary between acceptable use and missed specificity. When the record supports a more precise code, assigning I38 is a coding error even if the claim pays.

Includes notes: What falls under I38

The ICD-10-CM tabular list specifies six inclusion terms for I38. Each covers an endocarditis or valve presentation documented with no cause, no organism, and no named valve.

• Endocarditis (chronic) NOS – inflammation of the endocardium documented as chronic, or without further specification of organism or affected valve
• Valvular incompetence NOS – a valve that fails to close properly, with no valve or cause specified
• Valvular insufficiency NOS – a valve unable to prevent backflow, with no valve or cause specified
• Valvular regurgitation NOS – backward blood flow through a valve, with no valve or cause specified
• Valvular stenosis NOS – narrowing of a valve opening, with no valve or cause specified
• Valvulitis (chronic) NOS – chronic inflammation of a heart valve, with no valve or cause specified

All six terms share the same pattern: no valve is named, and no organism or rheumatic cause is documented. Where the record adds any of those details, a more specific code applies instead. Examples include I33.0 for an infective cause or an I34-I37 code for a named valve.

Excludes1 notes: Conditions ruled out for I38

I38 carries an Excludes1 note, which is a hard exclusion. Excludes1 means the listed conditions cannot be coded at the same encounter as I38 because they are mutually exclusive. If the documentation supports any of the excluded codes, assign that code instead of I38, never both.

Misinterpreting Excludes1 as Excludes2 is a serious coding error. Excludes2 indicates a condition is not included here but may coexist and be coded simultaneously. Excludes1 is never a “code both” scenario.

I33 (infective endocarditis) and I39 (endocarditis in diseases classified elsewhere) are not on this list. Both sections below cover them as differential picks, not formal exclusions. Solid denial management workflows catch a wrong pick before claims submit, but the fix belongs at documentation level, not at the clearinghouse.

Approximate synonyms and clinical terms for I38

The ICD-10-CM alphabetical index recognizes several terms that map to I38. Knowing these synonyms helps coders search efficiently and helps clinicians understand which documentation phrases trigger the unspecified code rather than a more precise one.

• Endocarditis NOS
• Endocarditis, chronic NOS
• Valvular heart disease NOS
• Valvular heart disease, chronic NOS
• Endocarditis (chronic)

The phrase “NOS” (not otherwise specified) is the common denominator. Any documentation that uses these exact terms without additional clinical context will correctly resolve to I38 under the alphabetical index. Here is the practical implication. If a physician dictates “chronic endocarditis” without naming the valve or the organism, the coder’s only option is I38. That holds regardless of what may be clinically implied.

Related ICD-10 codes: Parent, adjacent, and frequently confused codes

I38 sits in a family of endocarditis and valvular heart disease codes. Selecting the right code requires knowing which adjacent codes exist and what distinguishes each from I38.

I38 vs I33: Choosing between unspecified and infective endocarditis

I33.0 (acute and subacute infective endocarditis) and I38 are the two codes coders most commonly confuse. The decision rule is straightforward: if the clinician has identified or suspected a causative organism, or has documented an acute or subacute presentation, I33.0 applies. I38 is only correct when neither criterion is met.

A practical example: a patient is admitted with fever, positive blood cultures for Streptococcus viridans, and echocardiographic vegetations. The physician documents “endocarditis.” Despite the vague wording, the clinical evidence establishes an infective cause. Code I33.0, not I38. The coder should query the physician if the documentation alone would otherwise force an unspecified assignment.

I38 vs I39: Endocarditis in diseases classified elsewhere

I39 is a manifestation code for endocarditis that develops from a systemic disease coded elsewhere in the record. It is not on I38’s Excludes1 list. A coder should still use it instead of I38 whenever a codable underlying disease is documented, sequencing that disease first.

The clearest example is endocarditis caused by Q fever: code A78 first for the Q fever, then I39 for the endocarditis it produced. Two conditions coders often mix up with I39 do not belong there at all. Libman-Sacks endocarditis in lupus has its own combination code, M32.11, and is specifically excluded from I39. Marantic (nonbacterial thrombotic) endocarditis also does not route to I39. The alphabetic index maps it to I38 itself, so a coexisting malignancy gets its own separate code alongside I38.

Documentation requirements for assigning ICD-10 code I38

I38 is a code of exclusion. The documentation must confirm the absence of four conditions before a coder can defensibly assign it. Think of the assignment criteria in negative terms: what is not documented, not what is.

• No specified valve: the record does not name the aortic, mitral, tricuspid, or pulmonary valve, which would route to an I34-I37 code instead
• No congenital or fibroelastosis cause: the valve dysfunction is not documented as congenital (Q24.8) or as endocardial fibroelastosis (I42.4), I38’s two structural Excludes1 codes
• No rheumatic cause: the record does not attribute the endocarditis to rheumatic disease (I09.1), I38’s Excludes1 code for cause
• No causative organism, acute onset, or systemic disease documented: none of these formally excludes I38, but a coder should still rule out I33.0 and I39

When all four are absent from the record, I38 is the correct assignment. When any one is present, the coder must escalate to a more specific code or issue a physician query. Coding guidance from the AAPC reinforces that NOS codes are residual categories, not defaults for incomplete workups.

Coders working with other NOS-heavy code families will recognize this pattern. An NOS code is never a substitute for a clinician query when the record implies greater specificity.

Stop defaulting to unspecified codes

Pabau’s integrated clinical documentation tools prompt clinicians for organism, valve site, and etiology at the point of care. That level of detail keeps coders from defaulting to I38 when a sharper code applies.

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Medical billing and claims: Using ICD-10 code I38 for reimbursement

I38 is valid for HIPAA-covered electronic transactions, confirmed by the CDC/NCHS ICD-10-CM web tool. It can be submitted as a principal or secondary diagnosis on the CMS-1500 (837P professional claims) and UB-04 (837I institutional claims). Understanding how medical billing works for NOS-category codes is essential before submitting.

Pabau integrates with electronic claims via Claim.MD, Pabau’s US clearinghouse partner, supporting real-time eligibility verification and electronic remittance processing across thousands of US payers. For cardiology-adjacent diagnoses like I38, real-time eligibility checks before the encounter confirm whether the payer requires prior authorization for the associated procedures.

A few payor considerations apply specifically to I38. Because it is an unspecified code, some Medicare Administrative Contractors (MACs) and commercial payers may flag I38 claims for medical review. This risk rises when I38 is the primary diagnosis for high-cost cardiology procedures such as valve repair or replacement. The reason: payers expect specificity when the procedure itself implies a specific valve was treated. Submitting a clean claim with I38 alongside a procedure code that implies valve specificity is a documentation mismatch. That mismatch can trigger an Additional Development Request (ADR).

Pabau’s claims management software surfaces these mismatches before submission. The integration with HIPAA-compliant practice software workflows means documentation prompts appear at the point of care, not retrospectively during claim scrubbing.

ICD-10 code I38 history and FY2026 annual update

ICD-10 code I38 was not revised, deleted, or added in the FY2026 update cycle. It carries forward from prior fiscal years with its description, includes notes, and Excludes1 notes unchanged. The FY2026 edition became effective on October 1, 2025, per the annual CMS/NCHS release schedule.

CMS and NCHS co-maintain ICD-10-CM and release updates annually each October 1. Coders should verify code currency against the official CMS release each fiscal year. This matters most for codes adjacent to I38, such as I33, I34-I37, and I39, which have seen periodic description updates.

If you are reading this after October 1, 2026, check the FY2027 update first. Confirm I38 has not been revised before relying on the details in this reference. Pabau updates its internal code sets annually in line with CMS FY releases. Practices using Pabau’s integrated coding tools always work from the current version without manual cross-checks.

Conclusion

I38 is a legitimate, billable code, but treat it as a fallback rather than a default. Reach for it only once the record rules out a named valve, a causative organism, a rheumatic cause, and a documented underlying disease. Coding it too early risks a payer flagging the claim for review, particularly on high-cost cardiology procedures.

Pabau’s clinical documentation tools prompt clinicians for the specifics that distinguish I38 from I33.0, I39, and the valve-specific codes. That prompt happens at the point of care, not after the claim is submitted. See how Pabau handles revenue cycle documentation for cardiology and multi-specialty practices, or book a demo to review the diagnostic coding workflow.

Continue your research

Need to understand how denials are managed upstream? Denial management in healthcare covers the end-to-end workflow for catching and resolving claim denials before they age.

Want to see how electronic claims are submitted? 837 file formatting and submission explains how diagnosis codes like I38 map to the 837P professional claim transaction.

Looking for a broader cardiology coding overview? Medical billing compliance outlines documentation and submission standards that apply across ICD-10 cardiology diagnoses.

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