CPT code 83520 covers immunoassay measurement of analytes that are not infectious agent antibodies or antigens when no more specific CPT code applies. Nationally, this code matters because it provides a crosswalk for laboratory immunoassays that lack a dedicated code, affecting billing consistency and claims processing for clinical laboratories and hospital labs. Payers commonly involved in coverage and reimbursement for this code include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare.

Readers will learn what CPT code 83520 represents, the clinical and laboratory context in which it is used, and the types of benchmarks and policy considerations typically associated with unspecified analyte immunoassays. The publication covers billing practice implications, common modifier usage (listed separately), typical sites of service such as clinical and hospital laboratories, and where data is limited. The summary highlights that this code is applied based on methodology (immunoassay) and analyte type rather than a named test, which influences coding decisions and payer adjudication. Data not available in the input is noted where applicable.