HCPCS Level II code J1566 represents intravenous immune globulin in a lyophilized (powder) form, billed per 500 mg. This code is used nationwide for administration of immune globulin therapies in acute and chronic immunologic conditions where intravenous replacement or immunomodulation is required. Accurate use of this code affects clinical documentation, billing consistency, and payment integrity for infusion services across care settings. Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise explanation of the clinical context for immune globulin infusions, common sites of service, and which stakeholders typically manage coverage and payment. The publication reviews national benchmarking topics such as typical utilization units, common billing considerations, and payer policy themes. It also outlines relevant coding practice points, where available, and highlights areas where payers may differ on coverage criteria or documentation expectations. Data not available in the input is noted where applicable. This summary is intended to support billing managers, revenue cycle staff, and clinical leaders who oversee infusion therapies and reimbursement workflows.