Medical, surgical, diagnostic, and therapeutic procedures are coded using the CPT coding system. Developed by the American Medical Association (AMA), CPT codes consist of four numeric characters followed by a fifth alphanumeric character. Commonly used CPT codes include those for outpatient visits, surgical procedures, radiological tests, anesthetic procedures, history and physical examination, and emerging technologies. Unlike the ICD, the CPT is not a hierarchical coding system. Some concepts, however, have multiple codes depending on factors such as the visit length (for outpatient visits) or the amount of tissue removed (for surgical procedures).