Billing for nursing services-- question

[SHGR, MSN, RN, CNS]

How do other clinics bill for nursing services in outpatient/ambulatory care?

Do you use a point system, bill by amount of time spent, skill required, etc? I am talking about E&M codes, separate from G codes.

I spend a lot of time carefully documenting what I did to support any billing charges, but I still feel like I am underbilling for services provided. Most of what I do is chronic disease education. Some face-to-face visits and a lot of telephonic follow-up.

I did a lit search looking for validated tools that others may be using to use for billing, and came up empty- maybe I'm not using the right search terms or something?

Most of our clientele is T19. It can be very time-consuming and reimbursement is poor.

Any input is welcome. Thanks in advance.