Summary & Overview
CPT 84394: Total Tau Assay for Neurodegenerative Disease
CPT code 84394 represents a laboratory chemistry assay for measuring total tau, a biomarker used in the evaluation of neurodegenerative diseases such as Alzheimer’s disease. The test matters nationally because total tau measurement is increasingly incorporated into clinical assessment and research workflows to help characterize neuronal injury and disease progression. As biomarker-driven diagnosis and monitoring expand, coverage, coding clarity, and appropriate site-of-service billing become important for laboratories and clinicians.
Key payers included in this overview are Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise review of the clinical role of the test, expected service settings, common billing modifiers, and the types of documentation and ICD-10 diagnostic contexts that typically accompany orders. The publication also summarizes benchmarks and policy considerations relevant to laboratory billing, including common reimbursement pathways and payer authorization practices where applicable.
This resource is intended for billing professionals, laboratory managers, and clinicians to provide a clear national-level reference for coding and clinical context of CPT code 84394, helping stakeholders align documentation, billing processes, and clinical workflows for neurodegenerative disease biomarker testing.
Billing Code Overview
CPT code 84394 describes a laboratory chemistry test measuring total tau, a protein biomarker associated with neuronal injury and neurodegenerative disease. The test quantifies total tau concentration in biological specimens to assist clinicians in the diagnosis and monitoring of conditions such as Alzheimer’s disease, where elevated levels correlate with neuronal damage and cell death.
Service Type: Clinical laboratory testing — neurodegenerative disease biomarker assay
Typical Site of Service: Clinical laboratory or hospital laboratory; specimen collection may occur in outpatient clinics, neurology offices, or inpatient settings
Clinical & Coding Specifications
Clinical Context
A 72-year-old patient with progressive memory loss and impaired daily functioning is referred by a neurologist to the clinical laboratory for serum total tau testing as part of an evaluation for suspected Alzheimer disease and other neurodegenerative disorders. The clinician orders 84394 after a cognitive assessment and brain imaging suggest neurodegeneration; the patient presents to an outpatient phlebotomy suite in the hospital’s ambulatory care clinic. A trained phlebotomist obtains a venous blood specimen using standard precautions, labels the specimen with two patient identifiers, and sends it to the clinical chemistry laboratory. The lab analyst performs the total tau assay, documents instrument and reagent lot numbers, performs quality control, and reports a quantitative result in ng/L (or the assay’s unit). The neurologist reviews the result in the electronic medical record to support diagnostic interpretation, monitor disease progression, and correlate with clinical findings and imaging. Billing for the analytic test component is submitted under 84394 with the facility or laboratory taxonomies and the appropriate modifier to reflect professional or technical components as required.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
00 | No modifier used | Default reporting when no special circumstances apply |