Overview
CPT® code 83520 is used to report a quantitative immunoassay for analytes that do not have a specific CPT code assigned. Immunoassays are laboratory techniques that use the binding reaction between an antigen and an antibody to measure the concentration of a substance in a biological sample—typically serum, plasma, or other body fluids. This code applies when the test quantitatively measures a specific analyte using immunochemical methods and no more specific CPT code exists for that test.
When to Use CPT 83520
Use 83520 when performing a quantitative immunoassay for substances not covered by other analyte-specific codes. This might include hormone levels, specialized proteins, or other biomolecules that require precise quantification using immunologic detection methods. Common clinical applications include endocrine testing, autoimmune evaluations, or monitoring disease biomarkers in research or clinical settings.
Key Requirements
- The test must be quantitative, providing a measurable concentration of the analyte (not merely a positive/negative result).
- The analyte must lack a more specific CPT code—if one exists, that code should be reported instead.
- The test is typically performed on serum or plasma specimens.
- Documentation should clearly specify the analyte measured, the testing method, and the clinical reason for ordering the assay.
Billing Guidelines
- Report 83520 only when no other CPT code accurately describes the specific analyte tested.
- If multiple distinct analytes are tested using quantitative immunoassay methods, each analyte may be reported separately using 83520.
- Do not report 83520 for qualitative (yes/no) results—those are billed under separate immunoassay codes.
- Ensure that medical necessity is supported by the patient’s clinical presentation or physician documentation.
Example Clinical Scenarios
- A provider orders a quantitative immunoassay for a specialized hormone that lacks a dedicated CPT code.
- A research-driven clinical lab measures levels of a novel biomarker using a validated immunoassay method for diagnostic support.
- A physician monitors immune response or treatment effectiveness by measuring specific antibody concentrations quantitatively.
Summary
CPT® code 83520 is used for quantitative immunoassays of analytes that do not fall under existing, specific CPT codes. It ensures accurate billing and documentation when performing advanced or specialized immunoassay testing, particularly in endocrinology, immunology, or research-oriented diagnostic work.
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