Creatinine and Creatinine Clearance
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
How It Is Done
Collection of the blood sample
professional drawing blood will:
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure to the site and then a
Collection of the 24-hour urine sample
- You start collecting your urine in the
morning. When you first get up, empty your bladder but do not save this urine.
Write down the time that you urinated to mark the beginning of your 24-hour
- For the next 24 hours, collect all your urine.
Your doctor or lab will usually provide you with a large container that holds
about 1 gal (4 L). The container has a small amount of preservative in it.
Urinate into a small, clean container and then pour the urine into the large
container. Do not touch the inside of the container with your
- Keep the large container in the refrigerator for the 24
- Empty your bladder for the final time at or just before the
end of the 24-hour period. Add this urine to the large container and record the
- Do not get toilet paper, pubic hair, stool (feces), menstrual
blood, or other foreign matter in the urine sample.
How It Feels
The blood sample is taken from a vein
in your arm. An elastic band is wrapped around your upper arm. It may feel
tight. You may feel nothing at all from the needle, or you may feel a quick
sting or pinch.
There is no pain while collecting a
24-hour urine sample.
Risks of a blood test
There is very little chance
of a problem from having blood sample taken from a vein.
- You may get a small bruise at the site. You
can lower the chance of bruising by keeping pressure on the site for several
- In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.
- Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.
There is no chance for problems while
collecting a 24-hour urine sample.