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ICD-10-CM I21.29: ST elevation (STEMI) myocardial infarction involving other sites

I21.29 is the billable ICD-10-CM code for ST elevation (STEMI) myocardial infarction involving other sites, in category I21 (Acute myocardial infarction) of the Ischemic heart diseases section. As a principal diagnosis it groups to MS-DRG 280 Acute Myocardial Infarction, Discharged Alive with MCC, MS-DRG 281 Acute Myocardial Infarction, Discharged Alive with CC, MS-DRG 282 Acute Myocardial Infarction, Discharged Alive without CC/MCC (MDC 05 MDC 05: Diseases and Disorders of the Circulatory System). It maps to HCC 228 (Acute Myocardial Infarction) in CMS-HCC V28. As a secondary diagnosis it is an MCC, excluded with 25 principal diagnoses. 40 LCD billing and coding articles list it as covered.

Compiled from CMS files by the QuickIntell RCM Editorial Team · Data effective · Method: reference methodology · Report a data correction

Data currency: ICD-10-CM code descriptions: FY2027 (effective October 1, 2026); IPPS Table 5 (MS-DRG weights): v44 FY2027 (final rule + CN3) (effective October 1, 2026); ICD-10-CM to HCC mapping: PY2027 initial ICD-10-CM mappings (dates of service 2026) (payment year 2027); Medicare Coverage Database billing and coding articles: MCD release October 8, 2026 (effective October 4, 2026). Next CMS release: FY2028 code files, effective October 1, 2027 for the ICD-10-CM code descriptions; FY2028 final rule (August 2027), effective October 1, 2027; an April 1 interim grouper update when CMS issues one for the IPPS Table 5 (MS-DRG weights); PY2028 advance notice (February 2027) and the PY2027 midyear final mapping (spring 2027) for the ICD-10-CM to HCC mapping; weekly, every Thursday for the Medicare Coverage Database billing and coding articles.

Code
I21.29
billable FY2027 ICD-10-CM code
Category
I21 Acute myocardial infarction
Chapter
9: Diseases of the circulatory system (I00-I99)
CC/MCC (MS-DRG v44)
MCC
CMS-HCC V28
HCC 228
POA reporting
Required

Tabular list notes for I21.29

The tabular list has no notes on I21.29 itself; the notes below apply from its parent headings.

Inherited from I21 (Acute myocardial infarction)

Includes
  • cardiac infarction
  • coronary (artery) embolism
  • coronary (artery) occlusion
  • coronary (artery) rupture
  • coronary (artery) thrombosis
  • infarction of heart, myocardium, or ventricle
  • myocardial infarction specified as acute or with a stated duration of 4 weeks (28 days) or less from onset
Excludes2 (not part of this condition, may be coded together)
  • old myocardial infarction (I25.2)
  • postmyocardial infarction syndrome (I24.1)
  • subsequent type 1 myocardial infarction (I22.-)
Use additional code
  • 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)

Inherited from I21.2 (ST elevation (STEMI) myocardial infarction of other sites)

Inclusion terms
  • Type 1 ST elevation myocardial infarction of other sites

MS-DRG grouping when I21.29 is the principal diagnosis

MS-DRG v44 groups for I21.29 as principal diagnosis
MDCMS-DRGs
05 MDC 05: Diseases and Disorders of the Circulatory System280281282283284285

The final group also depends on procedures, secondary diagnoses and discharge status; the MS-DRG lookup for I21.29 shows the full grouping logic.

CC/MCC status and inpatient edits

As a secondary diagnosis, I21.29 is an MCC under MS-DRG v44, unless the principal diagnosis is one of the 25 codes in its exclusion list. Check I21.29 against a principal diagnosis.

  • Present on admission: a POA indicator is required on inpatient claims.

CMS-HCC V28 risk adjustment

In the PY2027 mapping, I21.29 maps to HCC 228 (Acute Myocardial Infarction). The HCC lookup shows the RAF weight and the hierarchy.

LCD billing and coding articles that list I21.29

40 current Medicare billing and coding articles list I21.29 among the diagnoses that support medical necessity for the services they cover.

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Frequently asked questions

What does ICD-10-CM I21.29 mean?

I21.29 means ST elevation (STEMI) myocardial infarction involving other sites. It is one of 13 billable codes under I21, acute myocardial infarction.

Which MS-DRG does I21.29 group to?

As the principal diagnosis, I21.29 groups to MS-DRG 280 Acute Myocardial Infarction, Discharged Alive with MCC, MS-DRG 281 Acute Myocardial Infarction, Discharged Alive with CC, MS-DRG 282 Acute Myocardial Infarction, Discharged Alive without CC/MCC (MDC 05 MDC 05: Diseases and Disorders of the Circulatory System) under MS-DRG v44, before procedures and secondary diagnoses are applied.

Does I21.29 map to an HCC?

Yes: HCC 228, Acute Myocardial Infarction, in the PY2027 CMS-HCC V28 mapping.

Is I21.29 a CC or MCC?

I21.29 is an MCC under MS-DRG v44; 25 principal diagnoses exclude it.

Sources

Every figure on this page is taken from the CMS publications below, as released by the Centers for Medicare & Medicaid Services. Projection built 2026-10-10. Verify against the primary file before billing or contracting decisions. The reference methodology explains how each figure is computed from these files.

Disclaimer

The descriptor and notes are reproduced from the FY2027 ICD-10-CM files; MS-DRG, CC/MCC and HCC facts come from the CMS FY2027 and PY2027 tables. Code from the medical record and the ICD-10-CM Official Guidelines. Not legal, clinical or billing advice.

Found a figure that does not match the CMS file? Report a data correction with the CMS file and the value you expected; the request reaches the editorial team through the contact form.