Urea Clearance

Timed urine specimen (usually 24 hours) and Serum (gold top tube) or Lithium Heparin Plasma (green top tube) specimen collected just before start of or during urine collection.

Collect a serum (gold top) or Lithium Heparin plasma (green top) tube at the start of urine collection or during urine collection.

Collect urine in a 24-hour urine jug and write start time and stop time or hours collected on jug.  If transferring an aliquot to a smaller container for transport, measure volume first and record on smaller specimen container, along with start and stop time or hours collected.  Timed specimens are typically collected for 24 hours, but can be collected in other increments, for example, 4 hours or 12 hours.

This test is for Urea Clearance.  To order Urine Urea without the clearance, order URUN, which does not require blood collection.  For Urea Nitrogen measurement on Plasma or Serum, order BUN.  For Urea Nitrogen measurement on Body Fluids, order MISUN.

Blood:  Serum (gold top) or Lithium Heparin Plasma (green top) tube
Urine:   24-hour urine container or sterile urine cup

Monday - Sunday, 8:00 am - 3:00 pm upon receipt

Urine Volume:     800 - 1800 mL/24 hours
Serum Urea:       7 - 17 mg/dL
Urea Clearance:  41 - 68 mL/min

Urea Clearance measures the amount of urea that is cleared from plasma by the kidneys in one minute.

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 which tend to increase urea excretion include increases in glomerular filtration rate, increased dietary protein intake, protein catabolic conditions, and water diuretic states.  Factors which reduce urea excretion include low protein intake and conditions which result in low urine output (eg, dehydration).

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 by taken into account when interpreting the results.

This test is for Urea Clearance.  To order Urine Urea without the clearance, order URUN, which does not require blood collection.  For Urea Nitrogen measurement on Plasma or Serum, order BUN.  For Urea Nitrogen measurement on Body Fluids, order MISUN.