SA Modifier

Needing some clarification on the use of this modifier. I know this is a Medicaid modifier and is used to report services performed by a Nurse Practitioner. This is usually used for TX Healthsteps, RHC's, and FQHC's. Medicaid manual just lists under those headings. I was under the impression this had to be used on all office visits, adult or child if a Nurse Practitioner sees. Can someone provide more clarification? This is Texas Medicaid.