CPT code 84393 represents a laboratory chemistry assay for phosphorylated tau proteins such as pTau-181 or pTau-217, biomarkers linked to tau pathology in Alzheimer disease and related neurodegenerative conditions. As interest in blood- and CSF-based tau assays grows, this code captures an emerging clinical diagnostic test with implications for neurologic evaluation, research, and potential targeted therapies. Nationally, the test is relevant for specialty neurology, memory clinics, and laboratory service lines seeking to incorporate tau biomarker testing into diagnostic workflows. Key payers discussed include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare.

Readers will learn the clinical context of the assay, its role in detecting tau-related pathology, and the typical clinical settings where the test is performed. The publication provides benchmark-oriented coverage information, common modifier usage, and operational considerations for laboratories and ordering clinicians. It also summarizes the clinical significance of phosphorylated tau measurement and what stakeholders should know about coding and billing for this laboratory chemistry service. Data not provided in the input are noted where applicable.