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Mayo Test ID URAU Urea, 24 Hour, Urine


Necessary Information


1. 24-Hour volume (in milliliters) is required.

2. For any timed collection the volume and length of collection is required.



Specimen Required


Supplies: Sarstedt 5 mL Aliquot Tube (T914)

Container/Tube: Plastic, urine tube

Specimen Volume: 4 mL

Collection Instructions:

1. Collect urine for 24 hours.

2. Mix well before taking aliquot.

Additional Information: See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens for multiple collections.


Useful For

Assessment of protein intake and/or nitrogen balance

Method Name

Photometric

Reporting Name

Urea, 24 HR, U

Specimen Type

Urine

Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time
Urine Refrigerated (preferred) 14 days
  Frozen  30 days
  Ambient  7 days

Reject Due To

All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

Clinical Information

Urea is a low molecular weight substance (60 Da) that is freely filtered by glomeruli, and the majority is excreted into the urine, although variable amounts are reabsorbed along the nephron. It is the major end product of protein metabolism in humans and other mammals. Approximately 50% of urinary solute excretion and 90% to 95% of total nitrogen excretion is composed of urea under normal conditions. Factors that tend to increase urea excretion include increases in glomerular filtration rate, increased dietary protein intake, protein catabolic conditions, and water diuretic states. Factors that reduce urea excretion include low protein intake and conditions that result in low urine output (eg, dehydration).

Reference Values

≥18 years: 7-42 g/24 hours

Reference values have not been established for patients who are less than 18 years of age.

Interpretation

Because multiple factors (glomerular filtration rate, dietary protein intake, protein catabolic rate, hydration state, etc.) can independently affect the urinary excretion of urea, all of these factors must be taken into account when interpreting the results.

Cautions

No significant cautionary statements

Clinical Reference

1. Lamb EJ, Jones GRD: Kidney function tests In: Rifai N, Horvath AR, Wittwer CT, eds. Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018:498-500

2. Bankir L, Trinh-Trang- Tan MM: Urea and the kidney. In: Brenner BM eds. The Kidney. 6th ed. WB Saunders Company; 2000

Method Description

Kinetic test with urease and glutamate dehydrogenase. Urea is hydrolyzed by urease to form ammonium and carbonate. In the second reaction 2-oxoglutarate reacts with ammonium in the presence of glutamate dehydrogenase and the coenzyme reduced nicotinamide adenine dinucleotide (NADH) to produce L-glutamate. In this reaction two moles of NADH are oxidized to NAD[+] for each mole of urea hydrolyzed. The rate of decrease in NADH concentrations is directly proportional to the urea concentration in the specimen and is measured photometrically.(Package insert: Urea/BUN reagent. Roche Diagnostics; 07/2024)

Specimen Retention Time

7 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

84540

LOINC Code Information

Test ID Test Order Name Order LOINC Value
URAU Urea, 24 HR, U 48999-7

 

Result ID Test Result Name Result LOINC Value
UREA Urea, 24 HR, U 48999-7
TM33 Collection Duration 13362-9
VL31 Urine Volume 3167-4
URECN Urea Concentration 63481-6

Day(s) Performed

Monday through Sunday

Report Available

Same day/1 day