Urine Test: 24-Hour Analysis for Kidney Stones

What It Is

A 24-hour urine analysis is sometimes a part of an evaluation of a child who has a kidney stone. This test measures how much urine (pee) a child produces in a day, the acidity (pH) of the urine, and the amount of certain substances in it, such as calcium, sodium, uric acid, oxalate, citrate, and creatinine.

Why It's Done

Kidney stones develop when certain salts or minerals build up in the urine and form crystals. The crystals stick together and enlarge, eventually forming a hard mass called a stone.

A 24-hour urine analysis can show if certain substances are found at high concentrations in the urine and might be causing the kidney stones. Urinary pH is also important, as certain crystals are more likely to form in urine that's too acidic (low pH) and others are more likely to form in urine that's not acidic enough (high pH).

The information from this test, in combination with other tests like blood tests and radiology studies, can help determine the cause and location of the stones and the treatment that might help prevent more kidney stones. Once treatment starts, another 24-hour urine collection can help determine whether the treatment is working.

Preparation

This test is usually done after a child has already passed a kidney stone and is feeling well, eating normally, and isn't being treated for a urinary tract infection (UTI). Your child might need to temporarily stop taking specific drugs that could interfere with test results. Be sure to review all your child's medications with your doctor.

The Procedure

Your doctor will give you a container in which to collect your child's urine over the course of 24 hours. Upon rising in the morning, your child will be asked to urinate into the toilet so that the test is begun with an empty bladder. You should note the exact time this is done — this is the start of your child's urine collection.

For the rest of the day, all of your child's urine should be collected in the container. The following morning, the first urine of the day should be collected as well, with the time of day recorded. During the testing period, all the urine should be collected, even if it is just a small amount.

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.

The container should be capped and kept in the refrigerator or a cool place during the collection period. Once all the urine has been collected, deliver the container to the lab your doctor recommended. It is important to follow all the instructions to correctly collect, store and transport the urine sample.

A laboratory technician will measure the urine volume and acidity level, and the amount of specific substances in the urine, and will report these findings to your doctor.

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. It's important to clean the area around the urinary opening before each urine sample is provided.

Getting the Results

The results of the 24-hour urine analysis will be available within a few days. If the test shows abnormal results, further tests may be needed. Talk to your doctor about the meaning of the specific test results.

Risks

No risks are associated with the 24-hour urine analysis. Infants may occasionally experience skin irritation from the adhesive tape on the collection bag. If a catheterized specimen is required it may cause temporary discomfort and you can discuss any questions you have about this procedure with your doctor.

Helping Your Child

The 24-hour urine analysis is painless. Explaining in simple terms 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 24-hour urine analysis, speak with your doctor.