CPT 0399U: Folate Receptor Antibody Test (FRAT®)

CPT code 0399U denotes the FRAT® (Folate Receptor Antibody Test), a proprietary ELISA-based laboratory assay from Religen Inc. that detects anti–human folate receptor IgG binding and blocking autoantibodies. As a PLA code, 0399U is unique to a single manufacturer’s test and is used when the assay has potential clinical implications for evaluation of autism spectrum disorder (ASD) and other neurodevelopmental conditions. Nationally, PLA codes like 0399U are important because they standardize billing for novel or single-source diagnostics and affect lab reporting, payer coverage determinations, and clinical use of targeted tests.

Key payers covered in this overview include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise summary of the test purpose and clinical context, the service and typical sites of service, and what to expect in payer coverage discussions. The publication outlines common modifiers associated with laboratory billing, notes that associated taxonomies, ICD-10 diagnoses, and related codes are not provided in the input, and directs readers to consult specific payer policies for coverage criteria and documentation requirements. The content is oriented to a national audience and focuses on how a PLA-coded diagnostic like 0399U fits into clinical workflows and reimbursement channels.

Billing Code Overview

CPT code 0399U is a Proprietary Laboratory Analyses (PLA) code that applies exclusively to the FRAT® (Folate Receptor Antibody Test) manufactured by Religen Inc. The test uses an enzyme–linked immunoassay (ELISA) to detect anti–human folate receptor IgG binding antibodies and blocking autoantibodies that affect folate metabolism. Results may have implications for evaluation of autism spectrum disorder (ASD) and other neurodevelopmental disorders.

Service type: Proprietary laboratory diagnostic test (PLA)

Typical site of service: Clinical laboratory or outpatient laboratory facility

Clinical Context

A pediatric neurology or developmental-behavioral clinic evaluates a 4–8 year-old child with global developmental delay, language regression, and social communication deficits concerning for autism spectrum disorder (ASD). The clinician documents a history of regression and possible response to folinic acid reported in family history. After clinical assessment, the clinician orders the FRAT® (Folate Receptor Antibody Test) to detect anti–human folate receptor IgG binding and blocking autoantibodies that may affect cerebral folate transport. Blood is drawn in the outpatient laboratory; the specimen is sent to Religen Inc. for Proprietary Laboratory Analysis. Results are returned as positive/negative for binding and blocking antibodies with titers, and are reviewed by the ordering clinician to inform discussion of folate metabolism implications in the child’s neurodevelopmental assessment and potential targeted interventions.

Coding Specifications

Modifier	Description	When to Use
`00`	No modifier — standard reporting	Use when no specific modifier applies and the test is reported as usual.
`26`	Professional component	Use if reporting only the professional interpretation component separate from the technical lab processing when applicable to billing arrangements.

Taxonomy Code	Specialty	Notes
2084P0800X	Pediatric Neurology	Common ordering specialty for neurodevelopmental assessments.
2084N0400X	Developmental-Behavioral Pediatrics	Frequently orders metabolic and antibody testing in ASD evaluations.
207Q00000X	Clinical Laboratory	Performing laboratory specialty for PLA testing and reporting.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`F84.0`	Autistic disorder	Common clinical indication for FRAT® testing given associations between folate receptor autoantibodies and autism spectrum disorder.
`F84.9`	Pervasive developmental disorder, unspecified	Used when developmental disorder is suspected but not fully specified; may prompt metabolic and antibody evaluation.
`R62.0`	Delayed milestone in childhood	Developmental delay is a typical scenario that can lead to ordering folate receptor antibody testing.
`F80.1`	Expressive language disorder	Language regression or impairments often prompt broader neurodevelopmental workup including folate-related testing.
`G31.84`	Mild cognitive impairment, so stated	Cognitive concerns may be part of the evaluation where folate receptor autoantibody testing is considered.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`0399U`	FRAT® (Folate Receptor Antibody Test) — enzyme–linked immunoassay for anti–human folate receptor IgG binding and blocking autoantibodies	Primary proprietary laboratory analysis described; report when Religen Inc. performs the FRAT® assay.
`80053`	Comprehensive metabolic panel	Often ordered concurrently to assess metabolic baseline and folate-related chemistries during neurodevelopmental evaluation.
`82746`	Folate; serum	Complementary laboratory measurement of serum folate level that may be ordered alongside antibody testing to evaluate folate status.
`81325`	CYP2D6 gene analysis (example pharmacogenomic test)	Example of other specialized laboratory tests that may be ordered in complex neurodevelopmental workups; illustrates laboratory coordination with PLA testing.

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Summary & Overview