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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 is 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 doctor 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 of 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 health care provider.

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

  • 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

  • Loss of potassium from a severe burn or draining wound

  • Diseases such as cystic fibrosis, primary aldosteronism, or alcoholismMedications such as diuretics or antibioticsGetting IV fluids without enough potassium

High blood potassium may be caused by:

  • Kidney failure

  • Trauma such as burns, accidents, or surgery

  • Uncontrolled diabetes

  • Diseases such as systemic lupus erythematosus, sickle cell, or Addison's 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 drugs can affect your potassium level, including penicillin, glucose, diuretics, and nonsteroidal anti-inflammatory drugs. 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 doctor if you are taking any medication, including over-the-counter NSAIDs.  In fact, be sure your doctor 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.