Current Procedural Terminology (CPT) code 90284 designates the supply of human immune globulin (SCIg) specifically formulated for subcutaneous administration. Immune globulin is a critical biologic therapy derived from the pooled plasma of thousands of healthy human donors, ensuring a broad and diverse spectrum of neutralizing immunoglobulin G (IgG) antibodies. This product provides essential passive immunity and is primarily indicated as a highly effective replacement therapy for patients suffering from primary humoral immunodeficiencies, such as common variable immunodeficiency (CVID), X-linked agammaglobulinemia, Wiskott-Aldrich syndrome, and severe combined immunodeficiency (SCID). Subcutaneous immune globulin offers significant clinical and lifestyle advantages over traditional intravenous immune globulin (IVIg) therapies. By delivering the medication directly into the subcutaneous adipose tissue, typically via a programmable infusion pump or manual push technique at sites such as the abdomen, thighs, or upper arms, SCIg allows for slower, more gradual systemic absorption. This physiological absorption profile leads to stable, more consistent serum IgG trough levels without the dramatic peaks and troughs frequently associated with monthly IVIg infusions. Consequently, patients often experience a marked reduction in systemic adverse events, such as severe headaches, myalgia, fatigue, and fever, while maintaining robust protection against debilitating bacterial and viral infections. Furthermore, SCIg formulations are specifically designed to facilitate self-administration in the home setting, thereby dramatically enhancing patient autonomy, convenience, and overall quality of life. From a technical and procedural standpoint, providing SCIg involves meticulous patient assessment, precise calculation of the weight-based dose, careful preparation of the biologic product to avoid protein degradation or foaming, and rigorous aseptic technique during the insertion of subcutaneous multi-needle sets. It is vital for medical coders and billing professionals to recognize that CPT code 90284 strictly represents the biologic product itself and does not encompass the clinical administration services. To achieve accurate and compliant reimbursement, the provision of the SCIg product must be billed in conjunction with the appropriate subcutaneous therapeutic infusion codes, such as 96369 for the initial hour of subcutaneous infusion and 96370 for each additional hour. Additionally, because many Medicare contractors and commercial insurance payers strictly mandate the use of highly specific HCPCS Level II J-codes to precisely identify the specific brand, concentration, and exact dosage of the administered immune globulin, thorough verification of payer-specific medical policies and formulary guidelines is absolutely essential prior to reporting 90284 on any medical claim.