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Potassium Test: About Your Child's Test

What is it?

A potassium test checks how much potassium is in your child's blood or urine. Potassium helps keep the body's water and electrolytes in balance. It is also important in how nerves and muscles work.

Your child’s doctor may ask for a urine or blood sample to test potassium levels. It can be checked in a single urine sample. But it's more often measured in a 24-hour urine sample.

Why is it done?

A blood or urine test for potassium may be done to:

  • Check to see how well your child's kidneys are working.
  • Check levels if your child is being treated with medicines such as diuretics. Or it can check levels if your child is having kidney dialysis.
  • See if treatment for low or high potassium levels is working.

How can you prepare for the test?

  • You don't need to do anything before your child has this test.
  • Be sure to tell the doctor about all the non-prescription and prescription medicines and natural health products your child takes. Many medicines and natural health product can affect the results of these tests.

What happens during the test?

Blood test

A health professional takes a sample of your child's blood.

One-time urine collection

If your child is old enough, he or she may follow the steps below without your help. If your child is younger, you will need to help.

  • You and your child should both wash your hands. Make sure that they're clean before you collect the urine.
  • If the collection cup has a lid, remove it carefully. Set it down with the inner surface up. Don't touch the inside of the cup with your fingers.
  • Clean the area around your child's genitals.
    • For a boy, pull back the foreskin, if your child has one, and clean the head of the penis with medicated towelettes or swabs.
    • For a girl, spread open the genital folds of skin with one hand. Then use the other hand to clean the area around the urethra with medicated towelettes or swabs. Wipe the area from front to back. This is so bacteria from the anus is not wiped across the urethra.
  • Ask your child to urinate into the toilet or urinal. A girl should hold apart the genital folds of skin while she urinates.
  • After the urine has flowed for a few seconds, place the collection cup into the urine stream. Collect about 60 mL of this "midstream" urine.
  • Don't touch the rim of the cup to the genital area. Don't get toilet paper, stool (feces), or anything else in the urine sample.
  • Have your child finish urinating into the toilet or urinal.
  • Carefully replace and tighten the lid on the cup. Then return it to the lab. If you are collecting your child's urine at home and can't get it to the lab in an hour, refrigerate it.

Urine collection over 24 hours

  • You and your child will start to collect the urine in the morning. When your child first gets up, have your child empty his or her bladder. But don't save this urine. Write down the time that your child urinated. This marks the start of the 24-hour collection period.
  • For the next 24 hours, collect all your child's urine. The large container from the doctor or lab has a small amount of preservative in it. Have your child urinate into a small, clean cup, and then pour the urine into the large container. Don't touch the inside of the container or the cup with your fingers.
  • Keep the large container in the refrigerator for the 24 hours.
  • Have your child empty his or her bladder for the last time at or just before the end of the 24-hour period. Add this urine to the large container, and record the time.
  • Don't get toilet paper, stool (feces), or other foreign matter in the urine sample.

How long does the test take?

A blood test or one-time urine collection will probably take a few minutes. Or you may collect your child's urine over a period of 24 hours.

Follow-up care is a key part of your child's treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse call line if your child is having problems. Ask your doctor when you can expect to have your child's test results.

Where can you learn more?

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