Summary & Overview

CPT 0500U: QClamp Plex UBA1 Mutation Test for VEXAS Syndrome

CPT code 0500U designates a Proprietary Laboratory Analyses (PLA) test: the QClamp® Plex VEXAS UBA1 Mutation Test from DiaCarta Inc., a targeted molecular assay that detects pathogenic variants in the UBA1 gene to aid diagnosis of VEXAS syndrome. As a PLA code, 0500U is unique to a single manufacturer's assay and carries implications for coding specificity, payer coverage policies, and laboratory reporting.

Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna, UnitedHealthcare, and Medicare. Readers will find a concise overview of how this PLA-designated CPT code fits into clinical practice for genetic diagnosis, typical sites of service for testing, and implications for national coverage frameworks. The publication highlights expected benchmarking areas such as coding accuracy, documentation practices, coverage policy considerations for proprietary tests, and potential policy updates that affect PLA-coded laboratory services.

The report provides clinical context on the test’s role in diagnosing VEXAS syndrome through targeted UBA1 variant detection, operational notes for laboratories and ordering clinicians, and an outline of common billing modifiers associated with laboratory services. Data not available in the input are clearly noted where applicable.

AetnaBlue Cross Blue ShieldCignaUnitedHealthcareMedicare0500UCPTProprietary Laboratory AnalysesGenetic TestingMolecular DiagnosticsVEXASUBA1Laboratory

Billing Code Overview

CPT code 0500U is a Proprietary Laboratory Analyses (PLA) code assigned to the QClamp® Plex VEXAS UBA1 Mutation Test from DiaCarta Inc. The code applies only to this single, manufacturer-specific laboratory test. The QClamp® Plex assay performs targeted variant analysis to detect specific mutations in the UBA1 gene used to diagnose VEXAS syndrome.

Service type: Targeted molecular genetic testing for UBA1 variants
Typical site of service: Clinical laboratory or reference laboratory performing specialized genetic testing

Clinical & Coding Specifications

Clinical Context

A 68-year-old male presents to a hematology clinic with a several-month history of refractory anemia, unexplained fevers, chondritis, skin lesions, and progressive cytopenias. He has a prior history of macrocytic anemia requiring transfusion and elevated inflammatory markers despite broad immunosuppressive therapy. The hematologist suspects VEXAS (Vacuoles, E1 enzyme, X-linked, Autoinflammatory, Somatic) syndrome and orders a targeted molecular assay to detect somatic UBA1 mutations.

The clinical workflow: the provider documents relevant signs (fever, chondritis, rash, cytopenias) and orders the QClamp® Plex VEXAS UBA1 Mutation Test using PLA code 0500U. A peripheral blood sample is collected in the clinic or outpatient laboratory and sent to the performing laboratory (DiaCarta Inc.) with required patient identifiers, clinical indication, and ICD-10 diagnosis codes. The laboratory performs targeted variant analysis for UBA1 somatic mutations, generates a molecular report including detected variants and interpretation, and returns results to the ordering clinician. Results inform diagnosis and management decisions such as referral to hematology, consideration of bone marrow biopsy, targeted therapies, or enrollment in clinical trials.

Coding Specifications

Modifier	Description	When to Use
`00`	Default/No modifier — standard reporting	Use when no specific billing modifier is applicable for the laboratory test.
`22`	Increased procedural services	Rarely applicable; use when additional, separately identifiable work beyond the typical test complexity is documented (e.g., extensive interpretation or consultation).
`26`	Professional component	Use when billing only the professional component (interpretation/reporting) separate from the technical component.
`52`	Reduced services	Use when the test is intentionally partially reduced or not completed as originally described.
`53`	Discontinued procedure	Use when test collection or processing was discontinued for patient-related or clinical reasons.
`62`	Two surgeons/dual provider	Uncommon for laboratory services; use only if two qualified practitioners share substantial responsibility for interpretation.
`78`	Unplanned return to the operating/procedure room	Not typically used for lab testing; include only if clinically justified in documentation.
`80`	Assistant surgeon	Not applicable for most lab tests; limited to operative services when an assistant surgeon is present.
`82`	Assistant surgeon (when qualified resident unavailable)	As above, generally not applicable to laboratory testing.
`QK`	Medical direction of two, three, or four ancillary personnel	Use if the ordering provider also medically directed multiple technical staff performing the test in a CLIA setting and payer requires this modifier.
`QX`	Modifier for solo practitioner to indicate the assistant performed services under QX arrangement	Rare for lab; include only if specific contractual arrangements require it.
`QY`	Attending provider signature for physician assistant services	Not typically applicable to lab billing; include per payer guidance if relevant.
`TC`	Technical component	Use when billing only the technical component (laboratory processing, sequencing) separate from professional interpretation.

Taxonomy Code	Specialty	Notes
207RH0000X	Hematology	Hematologists commonly order UBA1 testing for suspected VEXAS syndrome.
2080P0207X	Medical Oncology	Oncology/hematologic malignancy specialists may be involved when cytopenias or marrow abnormalities raise concern for myeloid neoplasia.
208D00000X	Pathology	Molecular pathologists or clinical laboratory directors oversee testing and interpretation of molecular assays.
363L00000X	Clinical Laboratory	Clinical laboratory directors and technologists perform and report the test under CLIA regulations.
207RN0400X	Rheumatology	Rheumatologists may order testing when patients present primarily with inflammatory features such as chondritis and vasculitis-like symptoms.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`D64.9`	Anemia, unspecified	Anemia is a common presenting feature in patients with VEXAS and often prompts molecular testing for UBA1 mutations.
`D61.9`	Aplastic anemia, unspecified	Bone marrow failure syndromes and cytopenias may lead clinicians to evaluate for somatic UBA1 mutations.
`M31.6`	Other necrotizing vasculopathies	VEXAS can present with vasculitic manifestations prompting molecular evaluation.
`M35.9`	Systemic involvement of connective tissue disease, unspecified	Inflammatory presentations resembling connective tissue disease may lead to UBA1 testing to distinguish VEXAS.
`R50.9`	Fever, unspecified	Unexplained fevers are a frequent clinical feature driving investigation for autoinflammatory syndromes including VEXAS.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`0500U`	QClamp® Plex VEXAS UBA1 Mutation Test — Proprietary Laboratory Analyses (PLA) code for targeted UBA1 variant detection	Primary billing code for the laboratory assay detecting UBA1 somatic mutations; used by the performing laboratory (DiaCarta Inc.).
`81210`	KRAS gene analysis; targeted sequence analysis (example of single gene mutation testing)	Serves as an example of a targeted single-gene molecular test; conceptually similar workflow (sample collection, sequencing, interpretation) though not specific to UBA1.
`81479`	Unlisted molecular pathology procedure	Use when a specific PLA or molecular test lacks an established code for payer adjudication or when additional unlisted molecular services are provided alongside `0500U`.
`0001U`	(Example PLA code) Proprietary laboratory analysis — other PLA codes may be billed for additional proprietary assays	Other PLA tests may be ordered concurrently for differential diagnostic evaluation; referenced as potential adjunctive molecular testing.
`88363`	Molecular pathology procedure; interpretation and report	Represents coding for professional interpretation and reporting of molecular test results when separating professional and technical components; may be used in conjunction with `0500U` if payer requires component billing.