Summary & Overview
CPT 82131: Quantitative Single Amino Acid Assay
CPT code 82131 represents a quantitative laboratory assay for a single amino acid, used to measure the concentration of a specific amino acid in blood, plasma, urine, or other body fluids. This targeted test is often performed after an abnormal screening result or when a clinician suspects a condition that can be diagnosed or monitored by an amino acid level. Nationally, single-analyte amino acid quantitation supports metabolic disorder diagnosis, therapeutic monitoring, and specialist-directed evaluation.
Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise overview of clinical context, common sites of service, and billing considerations tied to CPT code 82131. The publication summarizes typical use cases and what payers commonly review for coverage decisions, and provides benchmarks where available. It also outlines policy and coding updates relevant to laboratory services and highlights clinical scenarios in which single-amino-acid quantitation is most frequently ordered.
This summary is intended for laboratory managers, billing professionals, and clinicians seeking a national-level briefing on the purpose and application of CPT code 82131 without state-specific guidance.
Billing Code Overview
CPT code 82131 describes a quantitative assay for a single amino acid performed by a laboratory analyst on samples such as blood, plasma, urine, or other body fluids. The test measures the absolute concentration of a specific amino acid to confirm or quantify an abnormality identified on a prior screen or to support diagnosis of a condition in which that amino acid level is clinically relevant.
Service type: Clinical laboratory quantitative diagnostic test for a single analyte (amino acid)
Typical site of service: Clinical laboratory or hospital laboratory with specimen collection occurring in outpatient clinics, inpatient settings, or ambulatory collection sites
Clinical & Coding Specifications
Clinical Context
A pediatric or adult patient presents for quantitative amino acid testing after an abnormal newborn screen, metabolic screen, or when symptoms suggest an inborn error of metabolism, liver disease, renal tubular dysfunction, malnutrition, or certain aminoacidopathies. Typical presentation includes developmental delay, failure to thrive, seizures, vomiting, lethargy, unexplained encephalopathy, or features suggesting phenylketonuria, maple syrup urine disease, homocystinuria, or hyperammonemia. The ordering clinician (pediatrician, neonatologist, geneticist, metabolic specialist, or hospitalist) requests a single-amino-acid quantitative assay to confirm or monitor the level of a specific amino acid.
Sample collection is most commonly blood (plasma or serum), dried blood spot, or urine. The specimen is transported to a clinical chemistry or specialized metabolic laboratory. A medical laboratory scientist or lab analyst performs the quantitative assay using methods such as HPLC, tandem mass spectrometry, or enzymatic assays. Results are reported with numeric concentrations and reference ranges; critical values are communicated to the ordering clinician. Testing may be a follow-up after a screening panel, part of diagnostic workup, or used to monitor therapeutic response (dietary therapy or medical treatment). Typical sites of service include outpatient laboratory collection centers, hospital inpatient and emergency departments, neonatal screening programs, and specialty clinic phlebotomy areas.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 |