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Does this test have other names?

Serum potassium, serum electrolytes, K

What is this test?

This is a blood test to measure the amount of potassium in your blood. Potassium is one of several important minerals in your body called electrolytes. Ninety percent of your potassium is inside your cells, but a small amount circulates in your blood. You normally get potassium from your diet. Your body needs a constant level of potassium for normal nerve conduction, muscle contraction, heart function, and fluid balance. Your kidneys remove potassium through your urine. 

Why do I need this test?

You may have this test as part of a routine blood test to check your level of electrolytes. You may also need this test if your healthcare provider suspects that your potassium is too high or too low. It's important to have your potassium level checked if you have diabetes, if you have a disease that affects your kidneys, adrenal glands, or digestive system, or if you are on medications such as diuretics, steroids, or digitalis.

A potassium level that is too high is called hyperkalemia. Symptoms of hyperkalemia include:

  • Irregular heartbeat

  • Nausea

  • Fatigue

  • Tingling or numbness

  • Weakness or paralysis

A potassium level that is too low is called hypokalemia. Symptoms of hypokalemia include:

  • Irregular heartbeat

  • Nausea

  • Muscle weakness

  • Cramps

  • Constipation 

What other tests might I have along with this test?

You may have your potassium checked along with other electrolytes, such as sodium. You may also have an electrocardiogram, or ECG, to check your heart rhythm. An irregular heart rhythm is a dangerous sign if caused by an abnormal potassium level. 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

Potassium is measured in milliequivalents per liter (mEq/L). Normal results are about:

  • 3.5 to 5.2 mEq/L for adults

  • 3.4 to 4.7 mEq/L for children ages 1 to 18 years old

Low blood potassium may be caused by:

  • Loss of potassium from diarrhea, sweating, or vomiting

  • Not getting enough potassium in your diet. This is sometimes seen in alcoholism.

  • Loss of potassium from a severe burn or draining wound

  • Diseases such as cystic fibrosis, primary aldosteronism, or alcoholism

  • Medicines such as diuretics or antibiotics

  • Getting IV fluids without enough potassium

High blood potassium may be caused by:

  • Kidney disease or kidney failure

  • Trauma such as burns, accidents, or surgery

  • Uncontrolled diabetes

  • Diseases such as systemic lupus erythematosus, sickle cell, or Addison disease 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm. 

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Several medicines can affect your potassium level. These include penicillin, glucose, diuretics such as furosemide or hydrochlorothiazide, and nonsteroidal anti-inflammatory medicines. Eating a lot of licorice can decrease potassium levels.

How do I get ready for this test?

You don't need to prepare for this test. Tell your healthcare provider if you are taking any medicine, including over-the-counter NSAIDs. In fact, be sure your provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use. 

Online Medical Reviewer: Freeborn, Donna, PhD, CNM, FNP
Online Medical Reviewer: Hanrahan, John, MD
Date Last Reviewed: 8/31/2015
© 2000-2017 The StayWell Company, LLC. 800 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.