As coders, we like to know exactly what's new for each chapter of ICD-10-CM. What do we need to change from how we were assigning codes in ICD-9-CM? The good news is that for Chapter 9, there's not a great deal of change.
You will find that unlike ICD-9-CM, the type of hypertension is no longer used as an axis. In the past, you might have looked for terms such as "benign" or "malignant" within your documentation in order to assign either 401.0 or 401.1. This won't be an issue for you in ICD-10-CM. In the ICD-10-CM index you will see under hypertension that the ICD-10 code now includes accelerated, benign, essential, idiopathic, malignant, and systemic.
The acute myocardial infarction (MI) codes, also have been changed from eight weeks as demonstrated in ICD-9-CM down to four weeks or less for ICD-10-CM. So, for an initial MI, you will look to code I21 (keep an eye out for those that use additional code notations!) and for a subsequent MI, you will be directed to code I22. Please note, that a code from category I22 must be used in conjunction with a code from category I21 and that category I22 should never be used alone. The sequencing of these codes will be dependent upon the circumstances of the encounter.
The following algorithm may help you with code selection:
Patient admitted with AMI
|Previous MI?||No (I21 - initial MI)|
|Yes (Older than 28 days?|
|Yes (I21 - initial MI & I52.2 - old MI)||No (I22 - subsequent MI & I21 - initial MI)|