Urea Nitrogen, 24-Hour Urine (w/o Creatinine) (973X)

Test Code

7989N

CPT Codes
84540<br /> ** This test is not available for Florida, Rhode Island, Maryland, or New York patient testing **

Includes

CPT code 81050 may be added at an additional charge for volume measurement

Preferred Specimen

10 mL 24-hour urine or urine with no preservative in a plastic screw-cap container

Minimum Volume

2 mL

Other Acceptable Specimens

10 mL urine preserved with 6N HCL to maintain a pH of <6.0

Instructions

Refrigerate during and after collection. Record 24-hour urine volume on test request form and urine vial. Aliquot from a well-mixed 24-hour collection. Preserved urine may be shipped at room temperature.

Transport Temperature

Refrigerated (cold packs)

Specimen Stability

Room temperature: 24 hours
Refrigerated: 7 days
Frozen: 15 months

Methodology
Spectrophotometry (SP)

Setup Schedule

P.M. Sets up 5 days a week.

Clinical Significance

This quantitative urea nitrogen test, performed with a 24-hour urine specimen, may help estimate nitrogen balance and determine protein need in patients in critical conditions or receiving intravenous administration of nutrition [1].

Urea is the main nitrogen-containing product of protein breakdown and makes up over 75% of total nonprotein nitrogen excreted. Approximately 90% of the urea excretion is through the kidneys, and the rest is through gastrointestinal tract and skin. Because urea secretion is closely related to protein catabolism, urinary urea, commonly expressed by the concentration of urinary urea nitrogen, may be used to assess nitrogen balance and guide protein intake [1,2]. Blood and urinary urea levels were previously used as kidney function markers but are only considered useful in certain clinical scenarios; they have been generally replaced by creatine levels [1].

Urinary urea nitrogen level may be increased in individuals with hyperthyroidism or excess protein intake or breakdown [3]. It may be decreased in individuals with malnutrition, kidney damage or insufficiency, low-protein and high-carbohydrate diet, or liver disease. Pregnant persons and healthy children may also have low urinary nitrogen levels [3].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Lamb EJ, et al. Kidney function tests. Rifai N, et al. eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elservier Inc; 2022
2. Oh MS, et al. Evaluation of renal function, water, electrolytes, and acid-base balance. In: McPherson RA, et al, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021
3. Rao LV, et al. Laboratory tests. In: Rao LV, eds. Wallach's Interpretation of Diagnostic Tests. Pathways to Arriving at a Clinical Diagnosis. 11th ed. Wolters Kluwer; 2020.

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.