Modifiers in healthcare billing and coding are two-digit codes appended to CPT or HCPCS codes to provide additional information about the services or procedures performed. They indicate that a service or procedure has been altered in some way without changing its definition or the basic code itself. Modifiers help clarify circumstances that affect reimbursement or indicate special circumstances that may affect payment of the procedure.

For example, modifiers can indicate that multiple procedures were performed during the same session (modifier -59), that a service was provided at an unusual time (modifier -52), or that a service was reduced or discontinued (modifier -52 or -53). Proper use of modifiers ensures accurate billing and reimbursement by providing detailed information that reflects the complexity or specific circumstances of the healthcare services provided.