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I21.A ICD-10-CM Code: Other type of myocardial infarction

I21.A is not a CMS-HCC payment code. MEAT criteria · RAF Calculator · HCC coding software

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Code lookupI21.A

FY 2026 Apr update / Diseases of the circulatory system (I00-I99) / Ischemic heart diseases (I20-I25)

I21.A

Header CodeICD-10-CMOfficial ICD-10-CMCodebook guidance

Other type of myocardial infarction

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

N/A

—

Not mapped

CMS-HCC V24

N/A

—

Not mapped

ACA/HHS

N/A

—

Not mapped

ESRD/PACE

N/A

—

Not mapped

RXHCC

N/A

—

Not mapped

Code Book Path

Official
I21Acute myocardial infarctionI21.AOther type of myocardial infarction

Inclusion Terms

Official

No inclusion terms are included in this display for I21.A. Check the code and parent instructions in the Code Book.

Excludes 2

Official
  • certain conditions originating in the perinatal period (P04-P96)Inherited from I00-I99, I21
  • certain infectious and parasitic diseases (A00-B99)Inherited from I00-I99, I21
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)Inherited from I00-I99, I21
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)Inherited from I00-I99, I21
  • endocrine, nutritional and metabolic diseases (E00-E88)Inherited from I00-I99, I21
  • injury, poisoning and certain other consequences of external causes (S00-T88)Inherited from I00-I99, I21
  • neoplasms (C00-D49)Inherited from I00-I99, I21
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)Inherited from I00-I99, I21
  • systemic connective tissue disorders (M30-M36)Inherited from I00-I99, I21
  • transient cerebral ischemic attacks and related syndromes (G45.-)Inherited from I00-I99, I21
  • old myocardial infarction (I25.2)Inherited from I00-I99, I21
  • postmyocardial infarction syndrome (I24.1)Inherited from I00-I99, I21
  • subsequent type 1 myocardial infarction (I22.-)Inherited from I00-I99, I21

Related Codes

Official
I21.A1Myocardial infarction type 2I21.A9Other myocardial infarction type

Includes

Official
  • cardiac infarctionInherited from I21
  • coronary (artery) embolismInherited from I21
  • coronary (artery) occlusionInherited from I21
  • coronary (artery) ruptureInherited from I21
  • coronary (artery) thrombosisInherited from I21
  • infarction of heart, myocardium, or ventricleInherited from I21
  • myocardial infarction specified as acute or with a stated duration of 4 weeks (28 days) or less from onsetInherited from I21

Excludes 1

Official

No Excludes 1 notes are included in this display for I21.A. Check the code and parent instructions in the Code Book.

Code First

Official

No Code First sequencing instructions are included in this display for I21.A. Check the code and parent instructions in the Code Book.

Use Additional

Official
  • code, if applicable, to identify:Inherited from I21
  • exposure to environmental tobacco smoke (Z77.22)Inherited from I21
  • history of tobacco dependence (Z87.891)Inherited from I21
  • occupational exposure to environmental tobacco smoke (Z57.31)Inherited from I21
  • status post administration of tPA (rtPA) in a different facility within the last 24 hours prior to admission to current facility (Z92.82)Inherited from I21
  • tobacco dependence (F17.-)Inherited from I21
  • tobacco use (Z72.0)Inherited from I21

Code Also

Official
  • the presence of hypertension (I10-I1A)Inherited from I20-I25

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Code
I21.A
Description
Other type of myocardial infarction
HCC (V28)
No CMS-HCC V28 mapping
RAF reference coefficient
—
Billable
No
Payment year
2026

Coder workflow notes

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What This Code Means

I21.A is the ICD-10-CM diagnosis code for other type of myocardial infarction. I21.A sits in the ICD-10-CM chapter for diseases of the circulatory system (i00-i99), within the section covering ischemic heart diseases (i20-i25).

Header codes like I21.A cannot be reported on claims directly; they organize child codes that share clinical context. Coders should select the billable child code that matches the documented presentation and then verify its current source-backed HCC mapping. Do not infer a child code or risk adjustment value from the header alone.

HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for I21.A sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Child Codes

I21.A1Myocardial infarction type 2
HCC 228
I21.A9Other myocardial infarction type
HCC 228

Code Hierarchy

└I21Acute myocardial infarction└I21.AOther type of myocardial infarction
└I21.AOther type of myocardial infarction

I21.A code history

Code setChange
FY2018 (effective Oct 1, 2017)Added to the code set

Source: official CMS ICD-10-CM order and addenda files, FY2016 through FY2027.

Also searched as

  • I21 A
  • I21A

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