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ICD-10-CM 2027 diagnosis code

I21.BMyocardial infarction with coronary microvascular dysfunction

✓ Billable / specificMCC — major complication/comorbidity

I21.B is a valid, billable ICD-10-CM code for myocardial infarction with coronary microvascular dysfunction. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.Short description: Myocardial infarction with coronary microvascular dysfnct

Code last changed in FY2024 (effective October 1, 2023). Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About I21.B

I21.B is the ICD-10-CM diagnosis code for myocardial infarction with coronary microvascular dysfunction. It belongs to category I21 (acute myocardial infarction), block I20-I25 (ischemic heart diseases) and chapter 9 (diseases of the circulatory system). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Within I21 (acute myocardial infarction), I21.B is specifically for myocardial infarction with coronary microvascular dysfunction. Related codes cover ST elevation (STEMI) myocardial infarction of anterior wall (I21.0), ST elevation (STEMI) myocardial infarction of inferior wall (I21.1), ST elevation (STEMI) myocardial infarction of other sites (I21.2), ST elevation (STEMI) myocardial infarction of unspecified site (I21.3), Non-ST elevation (NSTEMI) myocardial infarction (I21.4), unspecified (I21.9) and other type of myocardial infarction (I21.A).

Use an additional 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.-) and 1 more.

As a secondary diagnosis it is an MCC (major complication or comorbidity), which can move an inpatient stay into the highest-paying "with MCC" MS-DRG of its family, unless the principal diagnosis excludes it.

In MS-DRG v44.0, it is part of the grouping logic for DRG 280 (Acute Myocardial Infarction, Discharged Alive with MCC, relative weight 1.6112), DRG 281 (Acute Myocardial Infarction, Discharged Alive with CC, relative weight 0.9184), DRG 282 (Acute Myocardial Infarction, Discharged Alive without CC/MCC, relative weight 0.7378), DRG 283 (Acute Myocardial Infarction, Expired with MCC, relative weight 1.9619), DRG 284 (Acute Myocardial Infarction, Expired with CC, relative weight 0.7525) and DRG 285 (Acute Myocardial Infarction, Expired without CC/MCC, relative weight 0.539), in MDC 05 (Diseases and Disorders of the Circulatory System), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

It was added in FY2024, effective October 1, 2023.

Coding notes

Applicable toConditions and synonyms classified to this code
  • Myocardial infarction with coronary microvascular disease
  • Myocardial infarction with nonobstructive coronary arteries [MINOCA] with microvascular disease

Notes that apply from higher levels

Instructions written at a parent level also apply to I21.B.

› 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
  • 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)

Broader instructions also apply from I20-I25 Ischemic heart diseases and Chapter 9: Diseases of the circulatory system.

Alphabetic index entries

5 entries

Terms in the official ICD-10-CM index that lead to I21.B.

Codes whose notes reference I21.B

MS-DRG v44.0 grouping

All DRGs →

Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.

Code history

  1. 2016
  2. 2017
  3. 2018
  4. 2019
  5. 2020
  6. 2021
  7. 2022
  8. 2023
  9. 2024
  10. 2025
  11. 2026
  12. 2027
  • FY2024 (effective 10/1/2023): Added
  • No changes since FY2024.

Common questions about I21.B

Is I21.B billable?

Yes. I21.B is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).

Can I21.B be used as a principal diagnosis?

Yes. The Medicare Code Editor doesn't restrict I21.B as a principal diagnosis.

Is I21.B a CC or MCC?

I21.B is an MCC (major complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.

What DRG does I21.B group to?

I21.B is used in the MS-DRG v44.0 logic for 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), MS-DRG 283 (Acute Myocardial Infarction, Expired with MCC), MS-DRG 284 (Acute Myocardial Infarction, Expired with CC) and MS-DRG 285 (Acute Myocardial Infarction, Expired without CC/MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.