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.
• For 24-hour urine collection, your doctor or lab will usually give you a large container that holds about 4 litres (1 gallon).

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. Open the wipes. Remove the lid from the container, and set it down with the inner surface up.
2. Wash your and your child's hands before you collect the urine.
3. Clean or have your child clean their genitals with the provided wipes. If your child has a vulva, hold the folds of skin or lips (labia) apart. Wipe the area from front to back. If your child has a penis, use the wipes to clean the tip. If your child has a foreskin, pull it back.
4. Ask your child to start urinating into the toilet for a few seconds. Keep holding their skin away from the urine stream.
5. After the urine has flowed for several seconds, place the collection container in the stream. Collect about 60 millilitres (2 ounces).
6. Don't let your child touch the container to their genitals.
7. Have your child finish urinating into the toilet or urinal.
8. Carefully replace the lid on the container.
9. Wash your and your child's hands.

How to do the test

Your 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 litres (1 gallon). A small amount of preservative may be in the container. You will use the container to collect your child's urine.

• When your 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.