Summary & Overview
CPT 0158U: MLH1 mRNA Sequence Analysis (CustomNext® + RNA)
CPT code 0158U is a Proprietary Laboratory Analyses (PLA) code for the CustomNext® + RNA: MLH1 test from Ambry Genetics®, used for mRNA sequence analysis of the MLH1 gene alongside the primary full-sequence analysis code. As a PLA code, 0158U identifies a single manufacturer- or lab-specific molecular diagnostic assay, making it important for lab reporting, claims processing, and manufacturer-specific coverage policies. Nationally, PLA codes like 0158U affect how payers and providers document test specificity and communicate clinical utility for hereditary cancer and genetic evaluation workflows.
Key payers discussed include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise overview of what the code represents, typical service settings, and the payer landscape relevant to this PLA molecular test. The publication also outlines benchmark considerations, policy and coverage update alerts, coding relationships with the primary full sequence analysis, and clinical context for MLH1 mRNA analysis in hereditary cancer evaluation. Data not available in the input is noted where applicable; the summary focuses on nationally relevant implications for billing, documentation, and payer engagement for this lab-specific molecular diagnostic code.
Billing Code Overview
CPT code 0158U is a Proprietary Laboratory Analyses (PLA) code that applies specifically to the CustomNext® + RNA: MLH1 test from Ambry Genetics®. The code is reported for mRNA sequence analysis of the MLH1 gene when performed in conjunction with the primary code for full sequence analysis. This PLA designation means the code represents a unique, manufacturer- or lab-specific molecular diagnostic assay.
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Service type: Laboratory molecular diagnostic testing for MLH1 mRNA sequence analysis
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Typical site of service: Clinical laboratory or reference laboratory setting
Clinical & Coding Specifications
Clinical Context
A patient with a personal or family history suggestive of Lynch syndrome (hereditary nonpolyposis colorectal cancer) is referred for germline evaluation. The referring clinician — often a medical geneticist, genetic counselor, oncologist, or colorectal surgeon — orders comprehensive DNA sequence analysis of mismatch repair genes and, when indicated by prior testing or suspected splicing variants, reflex or concurrent RNA-based analysis of MLH1 to clarify variant effect on mRNA splicing. Sample collection is via peripheral blood draw or clinically accepted specimen for Ambry Genetics®. The laboratory performs mRNA sequence analysis using the CustomNext® + RNA: MLH1 assay (0158U) in conjunction with the primary CPT code for full sequence analysis to characterize splice-altering variants or to resolve variants of uncertain significance. Results return to the ordering provider and genetic counselor for integration into diagnosis, cascade testing recommendations, and management planning. Typical site of service is an outpatient clinic, specialty genetics center, or a certified diagnostic laboratory performing proprietary testing.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | Use when reporting only the professional (interpretation) portion of the test if the laboratory separates technical and professional components and billing requires it. |