What modifier is used with add on codes?

The modifier commonly used with add-on codes is Modifier 51. This modifier indicates that multiple procedures are being performed during the same session, with one primary procedure and additional secondary procedures identified by the add-on codes. However, it's important to note that add-on codes themselves should not be reported with Modifier 51, as they are inherently understood to be additional procedures. Instead, the primary procedure should be marked with Modifier 51 if necessary.