Lupus Site - a guide for lupus patients and their families

This is a test of kidney function. It determines the amount of fluid filtered each minute by the kidneys. Creatinine is produced in the muscles and filtered through the kidneys. Almost all the creatinine released from the muscles makes its way into the urine. Comparing the amount of creatinine in the blood with the amount of creatinine in the urine gives an indication of kidney function.

This test is performed on a 24-hour urine sample. The person should follow the specific instructions of the healthcare provider on how to collect the urine sample. In general, this schedule is followed:
Day 1: The person urinates upon arising as usual. The person does not collect that sample. Then, the individual collects all urine produced for the next 24 hours in a special container.
Day 2: First thing in the morning, the person urinates into the container again. Then the individual covers it and refrigerates it. The sample is brought to the healthcare provider.

The person will also be required to give a blood sample so the blood level of creatinine can be measured and compared with that found in the 24-hour collection of urine.

Normal values for creatinine clearance (glomerular filtration rates) are as follows:
males, 97 to 137 milliliters/minute (ml/min)
females, 88 to 128 milliliters/minute

Abnormally low glomerular filtration rates may indicate:
- acute tubular necrosis, or kidney failure caused by damage to the kidney's tubules
- heart failure
- dehydration, or lack of fluids
- glomerulonephritis, or inflammation of the parts of the kidney that filter the blood
- inadequate blood flow to the kidneys
- shock, a life-threatening condition in which blood pressure falls too low to support life
- obstructive uropathy, a kidney disease caused by blockage of the kidney's drainage tubes
- acute nephrotic syndrome, the sudden inability of kidneys to perform their filtering role
- acute kidney failure
- kidney disease
- Wilms' tumor, a cancer of the kidneys generally seen in infants and young children