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Test Code RURAU Urea, Random, Urine

Reporting Name

Urea, Random, U

Useful For

Assessment of renal failure (prerenal vs acute kidney injury)

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type


Specimen Required

Container/Tube: Plastic, 5-mL tube (T465)

Specimen Volume: 4 mL

Collection Instructions:

1. Collect a random urine specimen.

2. No preservative.

Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Urine Refrigerated (preferred) 14 days
  Frozen  14 days

Reference Values

No established reference values

Day(s) and Time(s) Performed

Monday through Sunday; Continuously  

Test Classification

This test has been cleared, approved or is exempt by the U.S. 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


LOINC Code Information

Test ID Test Order Name Order LOINC Value
RURAU Urea, Random, U 44416-6


Result ID Test Result Name Result LOINC Value
URCON Urea, Random, U 3092-4
CREA5 Creatinine Concentration 2161-8
RATO4 Urea/Creatinine Ratio 44416-6

Clinical Information

Urea is a low molecular weight substance (Mol Wt=60) 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 which result in low urine output (eg, dehydration). Urea excretion is a useful marker of protein metabolism.


In oliguric patients with a rising creatinine a fractional excretion of urea <35% is consistent with a prerenal cause, while values >35% are more consistent with acute kidney injury.(2) The fractional excretion of sodium is also used for this purpose, but may be more affected by diuretics. Therefore, the fractional excretion of urea may be particularly useful for patients receiving diuretics.


Fractional excretion of urea <35% is consistent with a prerenal cause.

Clinical Reference

1. Carvounis CP, Nisar S, Guro-Razuman S: Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure, Kidney Int, 2002 Dec;62(6):2223-2229

2. Bankir L, Trinh-Trang-Tan MM: Urea and the kidney. In The Kidney. Sixth edition. Edited by BM Brenner. Philadelphia, WB Saunders Company, 2000

Analytic Time

Same day/1 day

Reject Due To

Hemolysis NA
Lipemia NA
Icterus NA
Other NA

Method Name

Kinetic Ultraviolet Assay