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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's also important in how nerves, heart, 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 do 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.

How is the test done?

Blood test

A health professional uses a needle to take a blood sample, usually from the arm.

Urine test

A urine test can be done using a single urine sample or urine collected over 24 hours. A single urine sample may be taken at a health professional's office or at home. A 24-hour sample is done at home.

How to do a potassium (K) clean-catch urine collection in children

  1. You and your child should both wash your hands before you collect the urine.
  2. Prepare the container.

    If the container has a lid, remove the lid and set it down with the inner surface up.

  3. Clean the area around your child's penis or vagina.
  4. Ask your child to urinate into the toilet or urinal.
  5. Collect the urine in the container.

    After the urine has flowed for several seconds, place the collection container in the stream. Collect about 60 mL (2 fl oz) of this "midstream" urine without stopping the flow. Don't touch the rim of the container to your child's genital area.

  6. Have your child finish urinating.
  7. Replace the lid on the container.
  8. Wash your and your child's hands.

How to do the test

You child's urine is collected for a period of time, such as over 4 or 24 hours. Your doctor will give you a large container that holds about 4 L (1 gal). You will use the container to collect your child's urine.

  • When you child first gets up, have them urinate.

    But don't save this urine. Write down the time your child urinated.

  • For the set period of time, collect all your child's urine.

    Each time your child urinates during this time period, collect the urine in a small, clean container. Then pour the urine into the large container. Don't touch the inside of either container with your fingers.

  • Don't let toilet paper, pubic hair, stool (feces), menstrual blood, or anything else get in the urine sample.
  • Keep the collected urine in the refrigerator for the collection time.
  • Have your child empty their bladder for the last time at or just before the end of the collection period.

    Add this urine to the large container. Then write down the time.

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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