What Is a Potassium Blood Test?

Medically Reviewed by Jennifer Robinson, MD on February 25, 2024
3 min read

In the right amounts, the mineral potassium helps your nerves and muscles “talk” to each other, moves nutrients into and waste out of your cells, and helps your heart function.

Kidney disease is a common cause of a high potassium level. Either high or low potassium levels can cause heart problems. Low potassium can cause muscle cramps.

You often have a blood test with your yearly physical that checks for your potassium levels. If you have any of the conditions mentioned above, your doctor may want you to be tested. The blood sample can check to see whether your potassium levels are in the normal range.

As a nutrient, potassium is found in a number of foods. Some foods with a lot of this mineral include:

  • Avocados
  • Bananas
  • Beets
  • Oranges and orange juice
  • Pumpkins
  • Spinach

Potassium is one mineral that plays an important role in controlling the amount of fluid in the body. Another is sodium. Too much sodium -- which the body mainly gets from salt -- leads to the body retaining fluid. This can lead to high blood pressure (hypertension) and other issues. Potassium balances the effects of sodium and helps keep fluid levels within a certain range.

Your body should maintain a specific amount of potassium in the blood, ranging from 3.6 to 5.2 millimoles per liter (mmol/L).

Your doctor may want you to get a blood test to check for potassium levels if they suspect you’re having health issues like:

Other terms used to describe this test are:

  • BMP (basic metabolic panel)
  • Chem 7
  • Electrolyte panel

In addition to potassium levels, the test may check your blood for chloride, sodium, and urea nitrogen (BUN).

Your doctor may ask you not to eat for at least 6 hours before the test, and to drink only water.

They’ll probably want to talk with you about your medical history and any medicines you’re taking. Some medicines may affect the results, so they might advise you not to take them before the test.

To do a test, a lab tech sticks a needle in a vein and takes a blood sample. Sometimes it’s hard to find a good vein, so they will tighten an elastic band around your upper arm and ask you to open and close your hand into a fist. The needle is attached to a tube, which collects the blood specimen.

This usually takes less than 5 minutes.

Blood tests are very common and have very few risks. However, any needle stick may cause bleeding, bruising, infection, or cause you to feel faint. Pay attention to the directions your doctor gives you, including applying pressure to the area and keeping it clean.

Depending on the lab, you should get the results back within a few days. (If there’s a lab at your doctor’s office, the results may be returned in less than an hour).

Your doctor will go over the results with you. If your potassium level is high (a condition called hyperkalemia) you may have:

If your potassium level is low (hypokalemia), you may have:

  • Kidney disease
  • Diabetic ketoacidosis
  • Folic acid deficiency (Folic acid is an important B vitamin that helps make new cells in your body.)

Hypokalemia may also be caused by:

Sometimes, a blood sample may be poorly taken or poorly tested, which can affect the test results. To make sure of the diagnosis, your doctor might ask you to take a second blood test. Or, they might ask you to take a urine test.

Patients who have already been diagnosed with kidney disease or other ailments may take potassium blood tests regularly.