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, and it is passed out of the body in urine.
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 relative amounts of other substances being excreted 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 an obstruction of the urinary tract. If test results are abnormal, other tests will be done to make a specific diagnosis.
A creatinine clearance test measures the blood creatinine level as well as how much creatinine is being passed in the urine over several hours. 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 dysfunction is suspected. Because creatinine is filtered out at a fairly steady rate, doctors compare the creatinine level with levels of other substances in the urine to determine if they're being excreted at a normal rate.
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.
Collecting the specimen should only take a few minutes. Your child will be asked to urinate into a clean sample cup in the doctor's office. If your child isn't potty trained and can't urinate into a cup, a small catheter may need to be inserted into the bladder to obtain the urine specimen.
If you collect the specimen at home, follow any storage and transportation instructions the lab gives you.
For a creatinine clearance test, you'll need to collect all the urine your child passes over a period of several hours (usually 24 hours). This usually involves first getting a special container from the lab in which to collect the urine, plus specific instructions about how to collect and store the timed urine sample.
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.
No risks are associated with taking a urine creatinine test.
Infants may occasionally experience skin irritation from the adhesive tape on the collection bag. If a catheter is used to obtain the urine, it may cause temporary discomfort. If you have any questions or concerns about this procedure, talk to your doctor.
Helping Your Child
Collecting the specimen for a urine creatinine test is usually painless. 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.
If You Have Questions
If you have questions about the urine creatinine test, speak with your doctor.