Creatinine and creatinine clearance tests measure the level of the
creatinine in your blood and urine. These tests tell
how well your kidneys are working. The substance creatine is formed when food
is changed into energy through a process called
metabolism. Creatine is broken down into another
substance called creatinine, which is taken out of your blood by the
kidneys and then passed out of your body in urine.
kidneys are damaged and can't work normally, the amount of creatinine in your
urine goes down while its level in your blood goes up.
types of tests on creatinine can be done:
Blood creatinine level
The blood creatinine level
shows how well your kidneys are working. A high creatinine level may mean your
kidneys are not working properly. The amount of creatinine in the blood depends
partly on the amount of muscle tissue you have. Men generally have higher
creatinine levels than women.
Creatinine clearance test
A creatinine clearance
test measures how well creatinine is removed from your blood by your kidneys. A
creatinine clearance test gives better information than a blood creatinine test
on how well your kidneys are working. A creatinine clearance test is done on
both a blood sample and on a sample of urine collected over 24 hours (24-hour
Blood urea nitrogen-to-creatinine ratio (BUN:creatinine)
The levels of blood creatinine and
blood urea nitrogen (BUN) can be used to find the
BUN-to-creatinine ratio. A BUN-to-creatinine ratio can help your doctor check
for problems, such as dehydration, that may cause abnormal BUN and creatinine
Urea is a waste product made when
protein is broken down in your body. Urea is made in the liver and passed out
of your body in the urine. A blood urea nitrogen (BUN) test measures the amount
of urea in your blood. Like creatinine, it can help your doctor see how well
your kidneys are working.
Why It Is Done
A blood creatinine level or a creatinine
clearance test is done to:
- See if your kidneys are working
- See if your kidney disease is changing.
how well the kidneys work in people who take medicines that can cause kidney
- Check for severe
dehydration. Dehydration generally causes
BUN levels to rise more than creatinine levels. This causes a high
BUN-to-creatinine ratio. Kidney disease or blockage of the flow of urine from
your kidney causes both BUN and creatinine levels to rise.
How To Prepare
Do not do any strenuous exercise for 2
days (48 hours) before having creatinine tests.
Do not eat more
than 8 oz (227 g) of meat,
especially beef, or other protein for 24 hours before the blood creatinine test
and during the creatinine clearance urine test.
Be sure to
drink enough fluids during the 24-hour urine collection but do not drink coffee
and tea. These are
diuretics that cause your body to pass more