Unlike most specialties, a single allergy encounter can combine an E&M visit, dozens of skin prick tests, intradermal testing, and an immunotherapy injection. Each of them has its own CPT code, unit count, and payer rules. Antigen preparation codes (95165) must be billed separately from administration (95115/95117), payer-specific panel limits how many allergens can be tested per session, and biologic drug billing includes J-codes and prior authorization. This gives you a billing environment where general coders consistently leave revenue on the table.