Is ICD-10-CM code I21 billable?

No, I21 (Acute myocardial infarction) is a non-billable ICD-10-CM code. It must be coded to a more specific subcategory before it can be used for reimbursement.

What chapter does ICD-10-CM code I21 belong to?

I21 belongs to Chapter 9 of the ICD-10-CM tabular list: I00–I99 (Diseases of the Circulatory System).

I21Not billable, use a more specific code below

Acute myocardial infarction

In Ischemic heart diseases (I20-I25), chapter 9: Diseases of the Circulatory System

13 billable codes under I21: all are an MCC; all map to HCC 228 (Acute Myocardial Infarction).A CC or MCC (major CC) is a secondary diagnosis that raises the MS-DRG payment. An HCC counts toward a Medicare Advantage patient's risk score.

Instructional notes

Includes: conditions that are coded here

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 included here, code separately if applicable

old myocardial infarction (I25.2)
postmyocardial infarction syndrome (I24.1)
subsequent type 1 myocardial infarction (I22.-)

Use additional code: add a second code for this, listed after this one

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)

Also applies, from Ischemic heart diseases (I20-I25)

These notes sit on I20-I25 and apply to every code under it, including I21.

Code also: add a code for this too, order depends on the encounter

the presence of hypertension (I10-I1A)

Official coding guidelines

From the ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027 (CMS and NCHS). Links open the PDF at the right page.

Section I.C.9.e Acute myocardial infarction (AMI) (page 54), covers I21
Report I21 codes while the MI is four weeks old or less; afterward use aftercare codes, or I25.2 for old MI. Use I22 with I21 only for a new type 1 or unspecified MI within four weeks.

All codes under I21

I21 can't be used on a claim. Pick a billable code below; grey headings group them.

I21 MS-DRGs

As the principal diagnosis, all 13 billable codes under I21 group to MS-DRG 280, 281, 282, 283, 284, or 285 (v44.0). Which one applies depends on procedures performed, secondary diagnoses (CC/MCC), and the patient's age and discharge status.

Other codes that refer to I21

Notes on these codes point to I21.

I16.1 Code Also: acute myocardial infarction (I21.-)
I5A Excludes1: acute myocardial infarction (I21.-)
I74 Excludes2: coronary embolism and thrombosis (I21-I25)
I82 Excludes2: coronary (I21-I25)
Z92.82 Code First: acute myocardial infarction (I21.-, I22.-)

About the condition

Plain-language background from MedlinePlus (National Library of Medicine), not coding guidance.

Heart Attack

A heart attack, also called a myocardial infarction, is a type of heart disease. It happens when blood flow to the heart suddenly becomes blocked. Without the blood coming in, the heart can't get oxygen. If not treated quickly, the heart muscle begins to die.

Code history

Valid since FY2016, when ICD-10-CM took effect on October 1, 2015.

FY2018: Title changed. It was: ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction.