Depends on what you are trying to charge.
On established patients they are 2 of 3, so as long as you have a chief complaint, you can level based on exam and MDM so you wouldn't "need" any HPI. Or you can code based on time, which doesn't require HPI either.
Now, based on the type of service you describe there probably isn't going to be any exam, so you either need to use time or have at least 1 element of HPI.
Laura, CPC, CPMA, CEMC