What Is a Potassium Blood Test?

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.

What Is Potassium?

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).

Why Would I Get This Test?

Your doctor may want you to get a blood test to check for potassium levels if she suspects 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).

How Do I Prepare?

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

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She’ll probably want to talk with you about your medical history and any medicines you’re taking. Some medicines may affect the results, so she 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 he 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.

What Do My Results Mean?

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, she 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.

WebMD Medical Reference Reviewed by Laura J. Martin, MD on January 22, 2017

Sources

SOURCES:

Royal Society of Chemistry: “Potassium.”

Lab Tests Online: “Potassium” (“The Test” tab).

National Health Service (UK): “Potassium test.”

Mayo Clinic: “Low potassium (hypokalemia),” “High potassium (hyperkalemia),” “High blood pressure (hypertension).”

Academy of Nutrition and Dietetics: “Kidney Disease: High- and Moderate-Potassium Foods.”

Blood Pressure Association (UK): “Why potassium helps to lower blood pressure.”

University of Rochester Medical Center: “Basic Metabolic Panel (Blood).”

National Heart, Lung, and Blood Institute: “What To Expect With Blood Tests.”

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