I21.9 — Acute myocardial infarction, unspecified
I21.9 is a billable, specific ICD-10-CM code for acute myocardial infarction, unspecified. It is valid for submission on a claim.
Inclusion terms
Alternative wordings a physician may use in the chart for this same code.
- Myocardial infarction (acute) NOS
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.
Medicare coverage
I21.9 is named in 32 Medicare coverage policies — 32 listing it as supporting medical necessity. Which of them applies to you depends on your Medicare contractor, and coverage genuinely differs by state.
- A52850Billing and Coding: Cardiac Catheterization and Coronary Angiography
- A52850Billing and Coding: Cardiac Catheterization and Coronary Angiography
- A56476Billing and Coding: Cardiac Radionuclide Imaging
- A56476Billing and Coding: Cardiac Radionuclide Imaging
How I21.9 is indexed
Coders do not find codes by browsing the tabular list — they look them up in the alphabetic index, under the word the physician wrote. These are the index entries that lead here, so you can see which chart wordings map to I21.9.
- Infarct, infarction›myocardium, myocardial(acute) (with stated duration of 4 weeks or less)
- Infarct, infarction›myocardium, myocardial›type 1
Related codes at this level
Codes that share I21. If I21.9 is not quite right, the correct code is usually one of these.
- I21.0ST elevation (STEMI) myocardial infarction of anterior wall
- I21.1ST elevation (STEMI) myocardial infarction of inferior wall
- I21.2ST elevation (STEMI) myocardial infarction of other sites
- I21.3ST elevation (STEMI) myocardial infarction of unspecified site
- I21.4Non-ST elevation (NSTEMI) myocardial infarction
- I21.AOther type of myocardial infarction
- I21.BMyocardial infarction with coronary microvascular dysfunction
Questions about I21.9
- Is I21.9 a billable ICD-10-CM code?
- Yes. I21.9 is a billable, specific ICD-10-CM code and is valid for submission on a claim.
- Where does I21.9 sit in the tabular list?
- Diseases of the circulatory system (I00-I99), in the block Ischemic heart diseases (I20-I25).