Potassium Blood Test

Urgent safety information

If you have symptoms such as arrhythmia (irregular heartbeat), severe muscle weakness, or numbness, seek emergency care. These symptoms may be related to abnormal potassium levels, but the test result itself does not require emergency action. Discuss your results with your provider.

Why this test may be ordered

• As part of a routine checkup
• To monitor an existing condition such as diabetes, kidney disease, or adrenal gland disorders
• If you take medicines that could affect potassium levels
• If you have symptoms of too much potassium (hyperkalemia) including arrhythmia, fatigue, muscle weakness, nausea, numbness or tingling
• If you have symptoms of too little potassium (hypokalemia) including irregular heartbeat, muscle cramps, weak or twitching muscles, fatigue, nausea, constipation

Preparation and collection

No special preparation is needed for a potassium blood test alone. If other tests are ordered on the same sample, you may need to fast (not eat or drink) for several hours before the test. Do not eat natural black licorice for at least two weeks before the test. Avoid repeated fist clenching during the blood draw.

A health care professional will take a blood sample from a vein in your arm. The procedure usually takes less than five minutes.

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.

Understanding results

Potassium levels that are too high or too low may be a sign of a medical condition and may cause serious health issues. However, not all abnormal results mean you have a condition that needs treatment.

• Normal potassium level: Your potassium level is within the normal range. Limitation: This result is based on a single blood sample and may vary with time or other factors. Next step: No specific follow-up is needed based on this result alone. Continue with routine care as directed by your provider.
• High potassium level (hyperkalemia): Your potassium level is higher than normal. Possible causes include kidney disease, Addison disease, injuries, burns, surgery, poorly controlled type 1 diabetes, or side effects of certain medicines. Eating very large amounts of potassium-rich foods or taking potassium supplements can also lead to high levels. Limitation: This result does not always mean you have a medical condition that needs treatment. Certain medicines or supplements may raise potassium levels. The lab result alone is not a diagnosis. Next step: Your provider will interpret this result in the context of your overall health and may recommend additional tests or adjustments to your treatment plan.
• Low potassium level (hypokalemia): Your potassium level is lower than normal. Possible causes include side effects of diuretics, fluid loss from diarrhea, vomiting, or heavy sweating, using too many laxatives, adrenal gland disorders (Cushing's syndrome, aldosteronism), kidney disease, alcohol use disorder, or a diet too low in potassium. Limitation: This result does not always mean you have a medical condition that needs treatment. Certain medicines (e.g., diuretics) or natural licorice can lower potassium levels. The lab result alone is not a diagnosis. Next step: Your provider will interpret this result in the context of your overall health and may recommend additional tests or adjustments to your treatment plan.

• Repeated clenching and relaxing of your fist just before or during the blood draw may temporarily increase potassium levels and lead to an incorrect result.
• Eating natural black licorice (not common in the U.S.) within two weeks before the test may lower potassium levels.
• Certain prescription and over-the-counter medicines and supplements can affect potassium levels.

What to do next

To learn what your results mean, talk with your provider. Your provider will interpret your results based on your health status, medications, and other factors.

• What is a potassium blood test?
• Why do I need a potassium blood test?
• What happens during a potassium blood test?
• Will I need to do anything to prepare for the test?
• Are there any risks to the test? What do the results mean?

Evidence source

U.S. National Library of Medicine: Potassium Blood Test