What is a potassium blood test?

A potassium blood test measures the amount of potassium in your blood. Potassium is a type of electrolyte. Electrolytes are electrically charged minerals that help control the amount of fluids and the balance of acids and bases (pH balance) in your body. They also help control muscle and nerve activity and perform other important functions.

Your cells, nerves, heart, and muscles need potassium to work properly. You can usually get most of the potassium that you need from the foods that you eat. Almost all of your body's potassium is inside your cells, but a small amount is in your blood. Your kidneys remove potassium in your urine (pee) to help keep the right amount of potassium in your blood. Potassium levels that are too high or too low may be a sign of a medical condition and may cause serious health issues.

Other names: potassium serum, serum potassium, serum electrolytes, K

What is it used for?

A potassium blood test measures the amount of potassium in your blood. The test is often part of a group of routine blood tests called an electrolyte panel. It may be used to monitor or diagnose conditions related to abnormal potassium levels. These conditions include kidney disease, high blood pressure, and heart disease.

Why do I need a potassium blood test?

Your health care provider may order a potassium blood test as part of your routine checkup or to monitor an existing condition, such as diabetes, kidney disease, or adrenal gland disorders. You may also need this test if you take medicines that could affect your potassium levels or if you have symptoms of having too much or too little potassium.

If your potassium levels are too high (hyperkalemia), your symptoms may include:

• Arrhythmia (a problem with the rate or rhythm of your heartbeat)
• Fatigue
• Muscle weakness
• Nausea
• Numbness or tingling

If your potassium levels are too low (hypokalemia), your symptoms may include:

• Irregular heartbeat
• Muscle cramps
• Weak or twitching muscles
• Fatigue
• Nausea
• Constipation

What happens during a potassium blood test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a potassium blood test or an electrolyte panel. If your provider has ordered more tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will let you know if there are any special instructions to follow.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Too much potassium in the blood (hyperkalemia) is often the result of two or more causes, which could include:

• Kidney disease. Too much potassium in your blood may mean your kidneys aren't working well.
• Addison disease, a disorder of the adrenal glands.
• Injuries, burns, or surgery, which can cause your cells to release extra potassium into your blood.
• Type 1 diabetes that is not well controlled.
• The side effects of certain medicines, such as diuretics ("water pills") or antibiotics.
• A diet too high in potassium (not common). Bananas, apricots, green leafy vegetables, avocados, and many other foods are good sources of potassium that are part of a healthy diet. But eating very large amounts of potassium-rich foods or taking potassium supplements can lead to health problems.

Too little potassium in the blood (hypokalemia) may be a sign of:

• The side effects of prescription diuretics
• Fluid loss from diarrhea, vomiting, or heavy sweating
• Using too many laxatives
• Adrenal gland disorders, including Cushing's syndrome and aldosteronism
• Kidney disease
• Alcohol use disorder (AUD)
• A diet too low in potassium (not common)

If your test results are not in the normal range, it doesn't always mean that you have a medical condition that needs treatment.

• Certain prescription and over-the-counter medicines and supplements may raise your potassium levels.
• You should not eat natural black licorice for at least two weeks before your test because it may lower your levels. Most licorice products in the U.S. don't contain natural licorice. But if you eat licorice, check the ingredients label to be sure.

To learn what your results mean, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a potassium blood test?

Repeated clenching and relaxing of your fist just before or during your blood test may temporarily increase the potassium levels in your blood. This may lead to an incorrect result.