CPT code 83527 describes a laboratory assay to measure free insulin concentration in a serum sample, representing the biologically active, unbound fraction of insulin; the service is a clinical laboratory quantitation performed by a lab analyst using specialized immunoassay or analytical chemistry methods, typically provided in an acute care hospital laboratory, independent clinical laboratory, or outpatient phlebotomy/diagnostic testing site for evaluation of insulin activity and metabolic status.

For related coverage guidance, see recent payer policy updates: Salivary Hormone Testing, Parathyroid Hormone, Phosphorus, Calcium, and Magnesium Testing, Bone Turnover Markers Testing.