Summary & Overview

CPT 0443U: Neurofilament Light Chain (NfL) Ultrasensitive Immunoassay

Headline: CPT code 0443U: Proprietary Neurofilament Light Chain Test for Nerve Injury

Lead: CPT code 0443U identifies a proprietary laboratory test — an ultrasensitive immunoassay for Neurofilament Light Chain (NfL) — offered only by the Neuromuscular Clinical Laboratory at Washington University in St. Louis School of Medicine. The test uses serum or cerebrospinal fluid to detect a biomarker of neuronal injury and is relevant to neurology diagnostics and monitoring.

CPT code 0443U represents a single-source Proprietary Laboratory Analyses (PLA) code for an NfL assay; such PLA codes are important because they designate unique tests tied to a specific laboratory or manufacturer. Nationally, NfL measurement is gaining clinical attention for its potential role in tracking neurodegenerative and neuroinflammatory conditions, making clear coding essential for billing clarity and utilization tracking. Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare.

Readers will learn the clinical context of the NfL assay, typical service settings, coding particulars tied to the PLA designation, and which payers are addressed. This publication provides benchmarks and policy-relevant context where available, summarizes typical billing considerations, and outlines what data are available versus missing. Data not available in the input are explicitly noted where applicable.

AetnaBlue Cross Blue ShieldCigna HealthUnitedHealthcareMedicare0443UCPTProprietary Laboratory AnalysesNeurofilament Light Chainultrasensitive immunoassayneurology diagnosticslaboratory testclinical laboratory

Billing Code Overview

CPT code 0443U is a Proprietary Laboratory Analyses (PLA) code that applies exclusively to the Neurofilament Light Chain (NfL) test performed by the Neuromuscular Clinical Laboratory at Washington University in St. Louis School of Medicine. The test measures NfL, a biomarker of nerve cell injury, using an ultrasensitive immunoassay on either serum or cerebrospinal fluid samples.

Service Type: Proprietary laboratory diagnostic test (ultrasensitive immunoassay for NfL)

Typical Site of Service: Clinical laboratory (sample collection may occur in outpatient phlebotomy, neurology clinic, or inpatient settings with specimens sent to the performing laboratory).

Clinical & Coding Specifications

Clinical Context

A patient with progressive neurologic symptoms such as unexplained gait instability, peripheral neuropathy, cognitive decline, or suspected neurodegenerative disease presents to a neurology clinic. The clinician orders the Neurofilament Light Chain (NfL) assay 0443U from the Neuromuscular Clinical Laboratory at Washington University in St. Louis School of Medicine to quantify NfL in serum or cerebrospinal fluid as a biomarker of neuronal injury. Typical workflow: clinician documents clinical concern and indications in the chart, obtains informed consent when collecting cerebrospinal fluid or draws a serum sample during a clinic visit or hospital encounter, labels and ships the specimen per lab instructions, and places the 0443U order in the laboratory system. Results return as a quantitative NfL concentration with interpretive guidance; the ordering neurologist integrates the result with imaging, electrophysiology, and clinical exam to assess disease activity, progression, or treatment response in conditions such as multiple sclerosis, amyotrophic lateral sclerosis, peripheral neuropathy, or other neurodegenerative disorders.

Coding Specifications

Modifier	Description	When to Use
`00`	No modifier (standard reporting)	Use when no specific billing modifier applies to the `0443U` laboratory test.
`22`	Increased procedural services	Use when documentation supports substantially greater lab processing or reporting effort beyond the usual for the assay.
`52`	Reduced services	Use when the test is performed but reduced or partially completed (for example limited specimen volume prevents full panel).
`53`	Discontinued procedure	Use when specimen collection or processing is begun but discontinued for documented clinical reasons.
`90`	Reference (outside) laboratory	Use when the performing laboratory acts as a reference lab and the service is billed by the ordering lab or facility.

Taxonomy Code	Specialty	Notes
2084P0800X	Neurology	Neurologists commonly order and interpret NfL testing for neurodegenerative and neuroinflammatory disorders.
207R00000X	Pathology	Clinical pathologists oversee specimen handling, assay validation, and result reporting for specialized lab tests.
208D00000X	Neuromuscular Medicine	Neuromuscular specialists use NfL to assess peripheral nerve and motor neuron injury.
207L00000X	Clinical Laboratory	Clinical laboratory directors and clinical chemists manage proprietary assay operations and quality control.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`G12.21`	Amyotrophic lateral sclerosis	NfL `0443U` may assist in assessing motor neuron injury and disease activity.
`G35`	Multiple sclerosis	NfL levels correlate with neuroaxonal damage and disease activity monitoring.
`G62.9`	Polyneuropathy, unspecified	NfL can indicate peripheral nerve injury severity.
`G31.9`	Degenerative disease of nervous system, unspecified	NfL may be used when evaluating suspected neurodegenerative conditions.
`R41.3`	Other amnesia	NfL testing can be part of workup when cognitive decline of unclear etiology is present.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`36415`	Collection of venous blood by venipuncture	Used to obtain serum sample for `0443U` when blood draw is required.
`59000`	Needle puncture of amniotic sac (obsolete example)	Data not available in the input.
`62270`	Spinal puncture, lumbar, diagnostic	Performed when cerebrospinal fluid is required for `0443U` testing.
`99000`	Handling and/or conveyance of specimen for transfer from site of collection to laboratory	Use when special specimen transport or handling is billed related to `0443U`.
`80053`	Comprehensive metabolic panel (example concurrent lab testing)	Often ordered alongside specialized biomarkers to assess systemic contributors to neurologic disease.