What It Is
Creatinine is a waste product that the muscles produce at a steady rate as part of normal daily activity. The bloodstream carries creatinine to the kidneys, which filter it out of the blood, then creatinine passes out of the body in the urine (pee).
A urine creatinine test measures the amount of creatinine in the urine. It can be done on its own or with other tests that determine the amounts of other substances in the urine.
Why It's Done
Healthy kidneys filter the blood to rid it of waste products that the body can't use. Low levels of creatinine in the urine may point to a kidney disease, certain muscular and neuromuscular disorders, or a blockage in the urinary tract. If test results are abnormal, other tests will be done to make a specific diagnosis.
A creatinine clearance test measures how much creatinine is passed in the urine over several hours. A blood test to measure the creatinine level in the blood is also usually done. This gives doctors information about how well the kidneys are functioning.
A doctor may order a urine creatinine test in combination with other urine tests even when no kidney problem is suspected. Because creatinine is filtered out at a fairly steady rate, doctors compare the creatinine level with levels of other substances to see if they're excreted at a normal rate.
Preparation
Your child might need to temporarily stop taking certain drugs that affect the urine's creatinine levels and might be asked to not eat large quantities of meat in the day or two before the test.
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The Procedure
For a creatinine clearance test, you'll need to collect all the urine your child passes usually over 24 hours. If you are doing this at home, this usually involves first getting a special container from the lab in which to collect the urine, plus specific instructions.
If your child isn't potty trained and can't urinate into a cup, urine collection bags with adhesive tape on one end might instead be used to collect the samples. Your baby's genital area will need to be cleaned, and then the bag is placed around the urinary opening and secured with the attached tape. A diaper can be placed over the bag. The bag will need to be changed frequently to collect all of the urine, and each bag will need to be emptied into the special container.
Another option is the use of a catheter (a narrow, soft tube), which can be inserted into the bladder and left there for 24 hours to obtain urine.
If you collect the specimen at home, follow any storage and transportation instructions the lab gives you.
What to Expect
Because the test involves normal urination, there shouldn't be any discomfort as long as your child can provide a urine specimen.
Getting the Results
In general, the results of the urine creatinine test are available within a day or two. Your doctor will go over the results with you and explain what they mean. If abnormalities are found, further tests may be needed.
Risks
No risks are associated with taking a urine creatinine test.
Infants may occasionally have skin irritation from the adhesive tape on the collection bag. If a catheter is used to get the urine, it may cause temporary discomfort. If you have any questions or concerns about this procedure, talk to your doctor.
Helping Your Child
Explaining how the test will be conducted and why it's being done can help ease any fear. Make sure your child understands that there should be no foreign matter, such as toilet paper or hair, in the sample. And all the urine should be collected for the test to be accurate.
If You Have Questions
If you have questions about the urine creatinine test, speak with your doctor.