Urea, Random, Urine
Assessment of renal failure (prerenal vs acute kidney injury)
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.
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
Fractional excretion of urea <35% is consistent with a prerenal cause.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
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