CPT code 86318 denotes a single-step immunoassay used to qualitatively or semiquantitatively detect antibodies in a patient specimen, most commonly blood. This laboratory procedure is widely used in infectious disease screening, serologic surveillance, and initial immune response assessment, making it relevant to public health monitoring and outpatient and inpatient diagnostic workflows nationwide. 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 purpose of the test, typical sites of service, and common billing considerations. The publication also summarizes available payer coverage patterns, common modifiers in use, and related billing considerations to aid coding accuracy and claims submission. Where specific payer policies or payment benchmarks exist, those are noted; if payer-specific data are unavailable, the report states that data are not available in the input. The content is intended to inform healthcare administrators, laboratory managers, and billing professionals about the clinical role of CPT code 86318, typical operational settings, and the topics to investigate further for payer-specific reimbursement and compliance guidance.