CPT code 84393 describes a laboratory chemistry assay for phosphorylated tau (for example, pTau 181 or pTau 217) measuring tau protein phosphorylation levels associated with neurodegenerative conditions such as Alzheimer’s disease; the service type is clinical laboratory testing and the typical site of service is an outpatient clinical laboratory or hospital laboratory where blood or cerebrospinal fluid specimens are analyzed by a lab analyst using immunoassay or similar chemistry methods.

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