Tennessee subscriber
Answer: Yes, you should take medical necessity into account. You must also consider physician intent. For example, some practices might report carotids with a noncovered diagnosis and then write off when the payer denies the claim. Others might choose not to report it, depending on the payer and physician's input.
Payers usually cover a look at the internal mammary arteries to see whether they are patent for future bypass. Try using the diagnosis for the catheterization on the left internal mammary artery (LIMA).
In the case you described, you'll need to dig a little deeper before you can begin coding, so find a time to consult the cardiologist. Ask him, were the carotids and subclavian done for a particular reason (such as, carotid bruit, syncope, or subclavian steal syndrome) or just because they were on the way to the LIMA? Cardiologists may dictate path and findings on subclavian when they are going to the LIMA. Remember that you do not bill the subclavian if the intent clearly is to get to the LIMA. Carriers would consider these guiding shots and not separately reimburse for them.