Summary & Overview
CPT 84540: Urine Urea Nitrogen Measurement
CPT code 84540 identifies a laboratory measurement of urea nitrogen in urine. This clinical laboratory test is used to evaluate renal function and nitrogen metabolism, supporting management of kidney disease, fluid and electrolyte disorders, and nutritional assessment. As a routine chemistry assay, the code is widely used across outpatient and inpatient laboratory settings and is relevant to hospitals, independent reference labs, and clinician-ordered testing.
Key payers in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. The publication provides national context on clinical use, billing and documentation considerations, and typical sites of service for the assay. Readers will find concise benchmarks for utilization and reimbursement where available, summaries of relevant billing guidance, and clinical context explaining when urine urea nitrogen measurement is ordered and how it informs patient care. Data not available in the input is noted where specific payer rates, taxonomies, or linked diagnosis codes would otherwise be expected. The focus is national rather than state-specific, intended for laboratory managers, billing professionals, and policy analysts seeking an operational and clinical overview of CPT code 84540.
Billing Code Overview
CPT code 84540 describes a laboratory assay in which a clinical laboratory analyst measures the amount of urea nitrogen in patient urine. The service is a clinical laboratory urine chemistry test used to assess renal function, nitrogen balance, and other metabolic conditions.
Service type: Clinical laboratory test — urine urea nitrogen measurement
Typical site of service: Clinical laboratory or hospital laboratory
Clinical & Coding Specifications
Clinical Context
A typical patient is an adult undergoing evaluation of renal function, fluid status, or suspected urea handling abnormalities. The clinician orders a urine urea nitrogen (UUN) test when monitoring patients with acute or chronic kidney disease, nephrotic syndrome, severe dehydration, or when calculating nitrogen balance in critically ill or malnourished patients. A sample is collected as a spot urine or 24-hour urine specimen in an outpatient laboratory, hospital clinical laboratory, or inpatient setting. The laboratory analyst performs 84540 to quantify urea nitrogen in the urine; results are reviewed by the ordering physician (nephrology, internal medicine, or hospitalist) to guide assessment of renal excretory function, protein catabolism, and nutritional status. Typical workflow: order placed in electronic health record, specimen labeled and transported to lab, technologist verifies specimen integrity, performs the UUN assay, documents results in the laboratory information system, and the clinician interprets results in the context of serum BUN, creatinine, and clinical status.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | Used when billing only the professional interpretation component if applicable (rare for automated lab tests). |
59 | Distinct procedural service | Used when is performed separately from another procedure on the same day and documentation supports distinct service.