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 urine.
How It Is Done
Collection of the blood sample
The health 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 alcohol.
Put the needle into the vein. More than one needle stick may be needed.
Attach a tube to the needle to fill it with blood.
Remove the band from your arm when enough blood is collected.
Put a gauze pad or cotton ball over the needle site as the needle is removed.
Put pressure on the site and then put on a bandage.
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 collection period.
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 fingers.
Keep the large container in the refrigerator for the 24 hours.
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 time.
Do not get toilet paper, pubic hair, stool (feces), menstrual blood, or other foreign matter in the urine sample.