Summary & Overview

CPT 83918: Total Organic Acids, 24-Hour Urine

CPT code 83918 denotes the laboratory measurement of total organic acids, most often performed on a 24-hour urine specimen. This biochemical assay evaluates metabolites derived from fatty acids, amino acids, carbohydrates, steroids, and hormones and is used in diagnostic evaluations for metabolic disorders, toxic exposures, and complex clinical presentations. Nationally, accurate coding and consistent use of this code support appropriate laboratory utilization tracking, clinical decision-making, and payer reimbursement processes.

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 for ordering the test, typical sites of service where the assay is performed, common billing modifiers and service-line considerations (Data not available in the input for payor-specific rates), and related administrative notes. The publication summarizes benchmarks and reporting considerations where available, highlights policy and coverage issues relevant to laboratory testing for metabolic evaluation, and outlines coding guidance and documentation points to support accurate claims submission.

This resource is intended for laboratory managers, billing professionals, clinicians ordering metabolic testing, and policy analysts seeking a national perspective on the clinical role and administrative handling of CPT code 83918. Data not available in the input for payer-specific reimbursement details and associated taxonomies.

AetnaBlue Cross Blue ShieldCigna HealthUnitedHealthcareMedicareCPT 83918total organic acidsurine organic acidsclinical laboratorymetabolic testinglaboratory billingtoxicologydiagnostic testing24-hour urine

Billing Code Overview

CPT code 83918 describes a laboratory measurement of total organic acids, typically performed on a 24-hour urine specimen. Total organic acids are metabolic byproducts derived from multiple biochemical sources, including fatty acids, amino acids, carbohydrates, steroids, and hormones. This test assesses organic acid levels to aid in metabolic evaluation and diagnostic workups.

Service Type: Clinical laboratory toxicology/metabolic analysis

Typical Site of Service: Clinical laboratory or hospital laboratory (specimens collected in outpatient clinics or inpatient settings and processed in a central lab)

Clinical & Coding Specifications

Clinical Context

A 7-year-old child with developmental regression, recurrent unexplained vomiting and failure to thrive is referred to a metabolic specialist. The clinician suspects an inborn error of metabolism or an acquired metabolic derangement affecting intermediary metabolism. A 24‑hour urine collection is ordered for 83918 (total organic acids) to quantify urinary organic acid metabolites that derive from amino acid, fatty acid, and carbohydrate catabolism. The clinical workflow: the clinician explains collection procedures to the family, provides a 24‑hour urine container and preservative instructions, and documents indications and relevant medications in the chart. The laboratory receives the specimen, verifies patient identifiers and collection adequacy, performs extraction and gas chromatography/mass spectrometry or similar analysis to measure organic acids, and generates a report. Results are reviewed by the ordering metabolic specialist or geneticist to correlate abnormal acidurias with specific metabolic disorders (for example, organic acidemias, mitochondrial disorders, or secondary disturbances due to toxin exposure), and to guide further targeted testing, dietary interventions, or referral to biochemical genetics.

Coding Specifications

Modifier	Description	When to Use
`26`	Professional component	Use when billing only the professional interpretation/reporting portion separated from the technical lab component.
`TC`	Technical component	Use when billing only the technical laboratory processing and reporting portion.
`90`	Reference (outside) laboratory	Use when the test was performed by an outside/reference laboratory and the ordering facility is billing for the service.
`91`	Repeat clinical diagnostic laboratory test	Use when a repeat measurement is performed on a subsequent specimen to confirm results within a short interval.
`52`	Reduced services	Use when specimen quantity or processing limitations require a reduced or partial testing panel.
`59`	Distinct procedural service	Use when multiple unrelated tests or procedures are billed the same day and separation is needed to indicate a distinct service.
`22`	Increased procedural services	Use when additional work or complexity beyond typical testing is documented (rare for standardized lab assays).
`90`	Duplicate listed above intentionally omitted per clinical relevance	Data integrity: do not duplicate entries.
`91`	Duplicate listed above intentionally omitted per clinical relevance	Data integrity: do not duplicate entries.
`00`	Default/No modifier	Use when no modifier is applicable and standard billing applies.

Taxonomy Code	Specialty	Notes
2080S0001X	Clinical Biochemist / Clinical Laboratory	Laboratory directors or specialists overseeing biochemical testing and interpretation.
208000000X	Clinical Pathology	Pathologists involved in laboratory oversight and result interpretation for metabolic testing.
207Q00000X	Pediatrics	Pediatricians who order and interpret metabolic screening tests in children.
2083P0207X	Clinical Geneticist	Medical geneticists or biochemical geneticists who diagnose inborn errors of metabolism.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`E71.3`	Disorders of branched-chain amino-acid metabolism	Organic acid testing detects abnormal metabolites such as branched-chain ketoacids seen in these disorders.
`E71.2`	Disorders of aromatic amino-acid metabolism	Identifies abnormal organic acids resulting from tyrosine/phenylalanine metabolism defects.
`E72.1`	Disorders of aromatic amino-acid metabolism (other)	Organic acid profiles assist in diagnosing varied amino-acid metabolic defects.
`E70.0`	Phenylketonuria	Urine organic acids can show intermediates or secondary metabolites relevant in workup.
`R11.2`	Nausea with vomiting, unspecified	Common presenting symptoms prompting metabolic urine organic acid testing.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`80048`	Basic metabolic panel	Often ordered concurrently to assess electrolytes and renal function that may influence organic acid interpretation.
`82043`	Blood ketone test, qualitative	May be ordered when ketosis is suspected, complementary to organic acid analysis.
`83013`	Hemoglobin A1c	Not routinely related but may be included in broader metabolic assessments in certain clinical contexts.
`82728`	Ammonia; quantitative	Ordered alongside `83918` when hyperammonemia or urea cycle disorder is in the differential diagnosis.
`81406`	Molecular pathology sequencing of panels (e.g., targeted panels)	May follow abnormal organic acid results to identify causative genetic variants in metabolic disorders.