Procedural code in the CPT book that is preceded with a plus (+) symbol indicating the code may be reported in addition to the parent or primary procedure code number (see Box A-1 ). Add-on codes are never reported for stand-alone services but are reported secondarily in addition to the primary procedure.Box A-1ADD-ON CODEParent code 11000Biopsy of skin … single lesion each separate/additional lesion (list separately in addition to code for primary procedure)Add-on code +11101