Mobile Site ›
Print Page Email Page

Interpretive Handbook

‹ Back to index | Back to list | More information

Test 89845:
Urea, Random, Urine

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

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.

Useful For Suggests clinical disorders or settings where the test may be helpful

Assessment of renal failure (prerenal vs acute kidney injury)

Interpretation Provides information to assist in interpretation of the test results

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

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

No established reference values

Clinical References Provides recommendations for further in-depth reading of a clinical nature

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