Test Details: 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. Measurement of serum urea has been used for many years as an indicator of kidney function. 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 (e.g. dehydration). Urea excretion is a useful marker of protein metabolism. In oliguric patients with a rising creatinine a fractional excretion of urea below 35% is consistent with a prerenal cause, while values above 35% are more consistent with acute kidney injury. 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. Urea measurement along with creatinine measurement may provide valuable clinical information. Increased urea with normal creatinine levels may be due to increased protein catabolism, dehydration, etc. An increase in both urea and creatinine may indicate malignancy, nephrolithiasis or prostatism. A decrease in both urea and creatinine may be due to acute tubular necrosis, liver disease, etc.