Summary & Overview
CPT 84393: Phosphorylated Tau Assay (pTau-181, pTau-217)
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.
Billing Code Overview
CPT code 84393 describes a laboratory chemistry assay for phosphorylated tau proteins, for example pTau-181 or pTau-217. The test measures levels of tau protein that have one or more phosphate groups attached; elevated phosphorylated tau can indicate tau aggregation and neurofibrillary tangle formation associated with Alzheimer disease and related neurodegenerative disorders.
Service type: Clinical laboratory chemistry assay
Typical site of service: Clinical laboratory or hospital laboratory
Data not available in the input.
Clinical & Coding Specifications
Clinical Context
A typical patient is an older adult referred to a memory disorders clinic for progressive cognitive decline, subjective memory complaints, or diagnostic uncertainty between Alzheimer disease and other neurodegenerative conditions. The neurologist or geriatrician obtains a detailed history, performs cognitive testing (e.g., MoCA, MMSE), orders brain imaging (MRI or CT) and lab tests. When biochemical biomarkers are indicated to support a diagnosis of Alzheimer disease or to discriminate Alzheimer pathology from other causes of dementia, the clinician orders a blood or CSF phosphorylated tau assay. In the laboratory, a clinical laboratory scientist or lab analyst performs the chemistry assay for phosphorylated tau (for example, pTau 181 or pTau 217) using validated immunoassays or mass spectrometry platforms. Results are reported to the ordering provider and incorporated into the diagnostic assessment and counseling for the patient and family. Typical site of service: outpatient hospital laboratory, independent clinical laboratory, academic medical center lab, or memory clinic associated lab.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
00 | No modifier / standard processing | Use when no special circumstances apply and full global service is reported |
26 |