Alternate Names : Glomerular Filtration Rate, GFR
This is a test of kidney function. It measures the amount
of fluid filtered each minute by the kidneys.
Creatinine is made in the muscles and filtered through
the kidneys. Almost all the creatinine released from the muscles makes
its way into the urine as a waste product. Comparing the amount of
creatinine in the blood with the amount of creatinine in the urine gives
an idea of how well the kidneys are functioning.
Who is a candidate for the test?
Anyone whose has kidneys that may not be functioning well
may need a creatinine clearance test.
How is the test performed?
This test is done with a urine sample gathered over a 24-
hour period. The person
should follow the specific instructions of the doctor on how to collect the
urine sample. In general, this schedule is followed:
Day 1: The person urinates upon arising without collecting that sample.
After that, he or she collects all of his or her urine
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 doctor, who will send it to the lab for analysis.
The person will also have a blood sample done
so the blood level of creatinine can be measured and compared with
that found in the 24-hour urine sample.