What is it?

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

Potassium levels can be tested with a blood test or a urine test. Urine potassium can be checked in a single urine sample. But it is more often measured in a 24-hour urine sample. Your doctor will decide if a urine or blood sample is needed.

Why is this test done?

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

• Check how well your kidneys are working.
• Check levels if you are being treated with medicines such as diuretics or having kidney dialysis.
• See if treatment for low or high potassium levels is working.

How do you prepare for the test?

• In general, there's nothing you have to do before this test, unless your doctor tells you to.
• For 24-hour urine collection, your doctor or lab will usually give you a large container that holds about 4 L (1 gal).

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 midstream urine collection

1. 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 penis or vagina.
4. Start 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 genital area.

6. Finish urinating.
7. Replace the lid on the container.
8. Wash your hands.

How to do the test

You collect your urine for a period of time, such as over 4 or 24 hours. Your doctor will give you a large container that holds about 1 gallon. You will use the container to collect your urine.

• When you first get up, you empty your bladder.

  But don't save this urine. Write down the time you began.

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

  Each time you urinate during this time period, collect your 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 get toilet paper, pubic hair, stool (feces), menstrual blood, or anything else in the urine sample.
• Keep the collected urine in the refrigerator for the collection time.
• Empty your 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 urine over a period of 24 hours.

What happens after the test?

After a blood test:

• You will probably be able to go home right away.
• You can go back to your usual activities right away.

After a urine test, you will need to return the urine sample to the lab or the doctor's office.