I21.9

I21.9: Acute myocardial infarction, unspecified

Billable / specific codeICD-10-CM

I21.9 is a billable, specific ICD-10-CM code for acute myocardial infarction, unspecified. It is valid for submission on a claim.

Check I21.9 with the rest of the claim: free scrubber

Inclusion terms

Alternative wordings a physician may use in the chart for this same code.

Myocardial infarction (acute) NOS

Excludes2 inherited from the categories above I21.9

Not part of this code, but both may be coded when both are present.

Written on I21: Acute myocardial infarction

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

Other codes that can never be billed with I21.9

Their own Excludes1 notes name this code, so the conflict is not listed above.

I5ANon-ischemic myocardial injury (non-traumatic)

Risk adjustment

I21.9 risk-adjusts. Under the CMS-HCC V28 model it maps to this category:

HCC 228 Acute Myocardial Infarction0.252 RAF

Coefficient shown for the Community Non-dual Aged segment. A higher HCC in the same hierarchy will suppress this one, so capturing it does not always add score. Look up the whole chart to see which of its HCCs the hierarchy would zero.

Medicare coverage

I21.9 is named in 23 Medicare coverage policies: 23 listing it as supporting medical necessity. Which one applies depends on your Medicare contractor.

A52850Billing and Coding: Cardiac Catheterization and Coronary Angiography
A56476Billing and Coding: Cardiac Radionuclide Imaging
A56602Billing and Coding: Cardiac Rhythm Device Evaluation
A56605Billing and Coding: B-type Natriuretic Peptide (BNP) Testing

Alphabetic index entries that lead here

Infarct, infarction›myocardium, myocardial(acute) (with stated duration of 4 weeks or less)
Infarct, infarction›myocardium, myocardial›type 1

Code history

Unchanged in every release from FY2024 to FY2027.