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I21.A9 vs I22.8

I21.A9 (Other myocardial infarction type) compared with I22.8 (Subsequent ST elevation (STEMI) myocardial infarction of other sites), from the official CMS tabular data.

Current data releases:ICD-10-CM FY2027 · ICD-10-PCS FY2027 · HCPCS October 2026 · MS-DRG v44 · Medicare Code Editor v44.0 · NCCI PTP Q4 2026 · MUE Q4 2026 · NCD code lists 2026-01 · LCD export September 28, 2026 · All releases and sources

Summary

These codes should not be reported together because I22.8’s tabular entry lists I21.A9 under Excludes1.

Official rule
What is different?

The conditions named.I21.A9 is “Other myocardial infarction type”; I22.8 is “Subsequent ST elevation (STEMI) myocardial infarction of other sites”.

Registry fact

Can these codes be reported together?

No.I22.8’s entry carries an Excludes1 note covering I21.A9: “subsequent myocardial infarction of other type (type 3) (type 4) (type 5) (I21.A9)”. Both may be reported only when the documentation shows the two conditions are unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Official ruleGuide: Excludes1 vs Excludes2

Is there an Excludes1 relationship?

Yes.I22.8’s tabular entry: “subsequent myocardial infarction of other type (type 3) (type 4) (type 5) (I21.A9)”. The note covers I21.A9.

Official ruleGuide: Excludes1 vs Excludes2

Is there an Excludes2 relationship?

Yes.I21.A9’s tabular entry: “subsequent type 1 myocardial infarction (I22.-)”. The note covers I22.8.

Official ruleGuide: Excludes1 vs Excludes2

Nothing found in 3 other checks; 1 check does not apply
Is one more specific?

Not comparable.The codes sit in different categories; specificity is only comparable within one category.

Is one a parent or header code?

No.Both are billable codes, and neither contains the other.

Registry fact

Are there sequencing instructions?

None.Neither entry carries a Code First or Use Additional Code note that names the other.

Official rule

Are there other coding relationships?

None found.No laterality, encounter-phase, Table of Neoplasms, Table of Drugs and Chemicals, or history-versus-active-disease relationship links these codes.

MedCoder-derived

Official rule: a tabular instructional note or a section of the ICD-10-CM Official Guidelines, quoted as published. Registry fact: the codes’ own published attributes (titles, billable status, position in the hierarchy, code set). MedCoder-derived: a reading MedCoder computes from those facts; it is not itself a rule. How to read the labels

Can these codes be reported together?

Excludes1 — generally not reported together

Excludes1 conflict

I22.8
Subsequent ST elevation (STEMI) myocardial infarction of other sites
↔
I21.A9
Other myocardial infarction type

What we found

No — do not report together.I22.8 carries an Excludes1 note covering I21.A9: “subsequent myocardial infarction of other type (type 3) (type 4) (type 5) (I21.A9)”

Sole exception: when the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

What to review

Report one of the two. Both may be reported only when the documentation shows the two conditions are unrelated to each other.

Guide: Excludes1 vs Excludes2Check these on a claim

Why it matters

An Excludes1 note means the two conditions are not ordinarily reported together for the same encounter, because the classification treats them as mutually exclusive forms of the same condition. The documented exception is when the two conditions are unrelated to each other.

Source / rule

CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a

Informational

Excludes2 relationship

I21.A9
Other myocardial infarction type
↔
I22.8
Subsequent ST elevation (STEMI) myocardial infarction of other sites

What we found

Yes, when both are documented.I21.A9 carries an Excludes2 note covering I22.8: “subsequent type 1 myocardial infarction (I22.-)”

Excludes2 marks distinct conditions — both may be reported when both are documented.

What to review

Report both only when the documentation supports both conditions; otherwise report the one documented.

Guide: Excludes1 vs Excludes2Check these on a claim

Why it matters

An Excludes2 note means the excluded condition is not part of the code above it, but a patient can have both. Report both when both are documented.

Source / rule

CMS ICD-10-CM tabular instructional notes

Official guidance behind these answers

  • Section I.A.12.a — Excludes1 · applies to: Excludes1

    A type 1 Excludes note is a pure excludes note. It means “NOT CODED HERE!” An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition. An exception to the Excludes1 definition is the circumstance when the two conditions are unrelated to each other. If it is not clear whether the two conditions involving an Excludes1 note are related or not, query the provider. For example, code F45.8, Other somatoform disorders, has an Excludes1 note for "sleep related teeth grinding (G47.63)," because "teeth grinding" is an inclusion term under F45.8. Only one of these two codes should be assigned for teeth grinding. However psychogenic dysmenorrhea is also an inclusion term under F45.8, and a patient could have both this condition and sleep related teeth grinding. In this case, the two conditions are clearly unrelated to each other, and so it would be appropriate to report F45.8 and G47.63 together.

    ICD-10-CM Official Guidelines FY2027

  • Section I.A.12.b — Excludes2 · applies to: Excludes2

    A type 2 Excludes note represents “Not included here.” An excludes2 note indicates that the condition excluded is not part of the condition represented by the code, but a patient may have both conditions at the same time. When an Excludes2 note appears under a code, it is acceptable to use both the code and the excluded code together, when appropriate.

    ICD-10-CM Official Guidelines FY2027

Quoted from the ICD-10-CM Official Guidelines for Coding and Reporting in effect for the release shown. The tabular notes above are the code-level instruction; these sections are the convention that says how such a note is applied. Source document (CMS PDF) · Release and checksum

Side by side

Similar descriptions do not make codes interchangeable. The documentation and the official instructions decide which code applies.

Official descriptionDiffers
I21.A9

Other myocardial infarction type

I22.8

Subsequent ST elevation (STEMI) myocardial infarction of other sites

StatusSame for both
Billable
Excludes1Differs
I21.A9

None at this code

I22.8
  • subsequent myocardial infarction, type 2 (I21.A1)
  • subsequent myocardial infarction of other type (type 3) (type 4) (type 5) (I21.A9)
Excludes2Differs
I21.A9
  • old myocardial infarction (I25.2)
  • postmyocardial infarction syndrome (I24.1)
  • subsequent type 1 myocardial infarction (I22.-)
I22.8

None at this code

Code firstDiffers
I21.A9
  • , if applicable, postprocedural myocardial infarction following cardiac surgery (I97.190), or postprocedural myocardial infarction during cardiac surgery (I97.790)
I22.8

None at this code

Use additional codeSame for both
  • code, if applicable, to identify:
  • exposure to environmental tobacco smoke (Z77.22)
  • history of tobacco dependence (Z87.891)
  • occupational exposure to environmental tobacco smoke (Z57.31)
  • status post administration of tPA (rtPA) in a different facility within the last 24 hours prior to admission to current facility (Z92.82)
  • tobacco dependence (F17.-)
  • tobacco use (Z72.0)
Code alsoDiffers
Only at I21.A9
  • complication, if known and applicable, such as:
  • (acute) stent occlusion (T82.897-)
  • (acute) stent stenosis (T82.855-)
  • (acute) stent thrombosis (T82.867-)
  • cardiac arrest due to underlying cardiac condition (I46.2)
  • complication of percutaneous coronary intervention (PCI) (I97.89)
  • occlusion of coronary artery bypass graft (T82.218-)
Only at I22.8

No note of its own beyond the shared notes

Shared by both codes (1 note)
  • the presence of hypertension (I10-I1A)
CategoryDiffers
I21.A9

I21 Acute myocardial infarction

I22.8

I22 Subsequent ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction

ChapterSame for both

I00-I99 — Diseases of the Circulatory System (I00-I99)

IncludesDiffers
Only at I21.A9
  • myocardial infarction specified as acute or with a stated duration of 4 weeks (28 days) or less from onset
  • Myocardial infarction associated with revascularization procedure
  • Myocardial infarction type 3
  • Myocardial infarction type 4a
  • Myocardial infarction type 4b
  • Myocardial infarction type 4c
  • Myocardial infarction type 5
Only at I22.8
  • acute myocardial infarction occurring within four weeks (28 days) of a previous acute myocardial infarction, regardless of site
  • recurrent myocardial infarction
  • reinfarction of myocardium
  • rupture of heart, myocardium, or ventricle
  • subsequent type 1 myocardial infarction
  • Subsequent acute transmural myocardial infarction of other sites
  • Subsequent apical-lateral transmural (Q wave) myocardial infarction (acute)
  • Subsequent basal-lateral transmural (Q wave) myocardial infarction (acute)
  • Subsequent high lateral transmural (Q wave) myocardial infarction (acute)
  • Subsequent transmural (Q wave) myocardial infarction (acute)(of) lateral (wall) NOS
  • Subsequent posterior (true) transmural (Q wave) myocardial infarction (acute)
  • Subsequent posterobasal transmural (Q wave) myocardial infarction (acute)
  • Subsequent posterolateral transmural (Q wave) myocardial infarction (acute)
  • Subsequent posteroseptal transmural (Q wave) myocardial infarction (acute)
  • Subsequent septal NOS transmural (Q wave) myocardial infarction (acute)
Shared by both codes (6 notes)
  • cardiac infarction
  • coronary (artery) embolism
  • coronary (artery) occlusion
  • coronary (artery) rupture
  • coronary (artery) thrombosis
  • infarction of heart, myocardium, or ventricle

No 7th character note at either code.

Notes are the code’s own tabular entry, quoted as published. A note that names the other code is the one the verdict above rests on. In a row that differs, each code’s own notes are listed under it, and the notes every code shares are listed once beneath them.

Derived from the official CMS ICD-10-CM tabular data (FY2027). A coding-rule comparison, not billing advice: payer-specific edits and medical-necessity policy are outside its scope. All data sources