Summary & Overview

CPT 83945: Urinary Oxalate Measurement, 24-Hour Specimen

CPT code 83945 identifies a quantitative laboratory assay for urinary oxalate, most commonly performed on a 24-hour urine specimen to assess oxalate excretion and risk for calcium oxalate kidney stones. Nationally, measurement of urinary oxalate is an established diagnostic tool in nephrology and metabolic stone clinics; accurate coding ensures appropriate laboratory reporting and coverage consideration across payers.

Key payers addressed include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find clinical context about when urinary oxalate testing is used, typical sites of service, and the role of the test in evaluating nephrolithiasis and metabolic disorders. The publication also summarizes common billing modifiers and notes where input data are unavailable.

This summary supports clinicians, laboratory managers, and billing staff by clarifying the test purpose and setting, outlining payer scope, and indicating the types of operational and policy content provided elsewhere in the publication, including benchmarking, coding guidance, and clinical interpretation considerations. Data not available in the input are identified and left for supplemental sections.

AetnaBlue Cross Blue ShieldCigna HealthUnitedHealthcareMedicare83945CPTurinary oxalatelaboratorynephrologystone diseaseclinical chemistry24-hour urinelaboratory billing

Billing Code Overview

CPT code 83945 describes a laboratory measurement of oxalate levels, typically performed on a 24-hour urine specimen. Oxalate is a naturally occurring compound found in certain foods (for example, some vegetables and nuts) and commonly appears in urine as calcium oxalate crystals. Measurement of urinary oxalate helps evaluate patients at risk for kidney stone formation and other disorders of oxalate metabolism.

Service type: Quantitative laboratory chemistry test
Typical site of service: Clinical laboratory or hospital outpatient laboratory

Clinical & Coding Specifications

Clinical Context

A typical patient is an adult referred to a clinical laboratory by a urologist or nephrologist for evaluation of recurrent nephrolithiasis (kidney stones) or unexplained hematuria. The clinician orders a 24-hour urine collection to quantify urinary oxalate excretion after initial imaging (CT or ultrasound) or stone analysis demonstrates calcium oxalate composition or when metabolic workup is indicated. The patient receives instructions for a complete 24-hour urine collection, dietary guidance to avoid excessive oxalate-rich foods during collection if required, and documentation of collection start and stop times. The specimen is delivered to the outpatient laboratory or hospital clinical chemistry department; the lab analyst performs the quantitative oxalate assay using an enzymatic or ion chromatography method. Results are reported to the ordering provider and used to guide dietary counseling, medical therapy (e.g., thiazide diuretics, citrate supplementation), or further metabolic evaluation. Typical sites of service include outpatient hospital laboratory, independent clinical laboratory, or hospital-based clinical chemistry lab within an ambulatory or inpatient facility.

Coding Specifications

Modifier	Description	When to Use
`26`	Professional component	When billing only the professional interpretation or oversight of a lab test if separated from technical component
`59`	Distinct procedural service	When the oxalate measurement is distinct from other billed lab procedures on the same day and needs to be identified as separate
`90`	Reference (outside) laboratory	When the specimen or test is sent to an outside reference laboratory for analysis
`91`	Repeat clinical diagnostic laboratory test	When the same oxalate test is repeated on a subsequent specimen for verifying results
`52`	Reduced services	When a modified or partial oxalate assay is performed yielding reduced service relative to full testing
`53`	Discontinued procedure	If the specimen is unsuitable and testing is discontinued prior to completion
`59`	Distinct procedural service	When testing is separate and unrelated to other services on the same date (listed twice here because of clinical relevance)
`90`	Reference (outside) laboratory	When sending to outside lab for confirmation or specialized methodology (duplicate for emphasis)
`91`	Repeat clinical diagnostic laboratory test	For confirmatory repeat 24-hour collections
`TC`	Technical component	When billing only the laboratory technical component separate from professional interpretation

Taxonomy Code	Specialty	Notes
207Q00000X	Clinical Laboratory	Clinical laboratory directors and pathologists overseeing quantitative urine testing
2080P0005X	Clinical Pathology	Pathologists who interpret complex metabolic testing and supervise lab methods
208000000X	Internal Medicine	Nephrologists or internists ordering metabolic stone evaluation
2083N0002X	Urology	Urologists ordering stone workup and correlating results with urologic care
207LP2900X	Laboratory Technician	Laboratory technologists performing the assay

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`N20.0`	Calculus of kidney	Common indication for measuring urinary oxalate to evaluate stone composition and recurrence risk
`N20.1`	Calculus of ureter	Used when ureteral stones are present to assess metabolic contributors including hyperoxaluria
`N20.2`	Calculus of kidney with calculus of ureter	Indicates stone disease involving multiple urinary tract sites prompting metabolic testing
`N20.9`	Urinary calculus, unspecified	General diagnosis prompting metabolic workup when stone etiology is unclear
`R31.0`	Gross hematuria	When hematuria coexists with suspected stones, oxalate testing may be part of broader workup
`E83.70`	Disorder of mineral metabolism, unspecified	Metabolic disorders affecting stone risk may prompt urine oxalate quantification
`E72.4`	Hyperoxaluria	Direct clinical indication for quantitative urinary oxalate testing

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`80053`	Comprehensive metabolic panel (CMP)	Performed to assess renal function and electrolytes during metabolic stone workup; often ordered alongside oxalate measurement
`82570`	Creatinine; urine (quantitative)	Used to normalize 24-hour urine analytes to creatinine or verify collection completeness
`82520`	Urine sodium; quantitative	Assesses dietary sodium which influences urinary calcium and stone risk in metabolic evaluation
`83945`	Oxalate; urine (quantitative)	Primary procedure measuring urinary oxalate excretion to evaluate calcium oxalate stone risk
`81025`	Urine pregnancy test, by dipstick or tablet reagent; non-automated	Often performed prior to imaging or certain interventions in reproductive-age patients (contextual adjunct)