How to Diagnose High Potassium Levels

Medically Reviewed by Nayana Ambardekar, MD on March 19, 2024
2 min read

Potassium is a nutrient in food that helps your body run smoothly. Too much potassium in your body can cause health problems, but a simple blood test can measure your levels.

Potassium plays a role in letting your muscles and nerves signal each other, keeps fluid levels balanced in your body, and helps you have a regular heartbeat. Your potassium levels might get high if your kidneys aren't working well.

A normal blood potassium level for adults is between 3.5 and 5.5 millimoles per liter (mmol/L).  

A potassium level above 5.5 mmol/L is high. Above 6.5 mmol/L is dangerously high and means you need medical care right away.

You often don't notice any symptoms from high potassium levels. You might first learn about it when you get the results of a routine blood test.

If you do get symptoms, they may come and go and might include:

  • Stomach pain
  • Diarrhea
  • Fatigue
  • Chest pain
  • Irregular heartbeat that may feel fast or like a fluttering sensation
  • Muscle weakness
  • Numbness or paralysis in your arms or legs
  • Nausea or vomiting

Check with your doctor if you have any of these symptoms, especially if you have kidney disease or take a medication that can raise your potassium level.

Your doctor will check your potassium level during your annual physical exam. If you have a health condition such as diabetes or kidney disease, they may test your potassium level more regularly. They will also see if you have symptoms of high potassium, high blood pressure, or signs of a heart problem.

To check for high potassium, you get a blood test which measures the amount of potassium in your blood. The doctor puts a small needle into a vein in your arm and takes out a small amount of blood. You might feel a slight pinch or sting when the needle goes in.

Your doctor sends the blood sample to a lab, where technicians test the level of potassium in the liquid part of your blood (serum). Your doctor will let you know the results.

It's not uncommon to have a false high potassium test result, which happens when blood cells rupture during the blood draw. They leak more potassium into your blood, making it seem like your level is high. Your doctor may repeat the test before treating you for high potassium.

If your doctor is concerned that you may be having a problem with your heart, they may also ask you to get a test called an electrocardiogram (EKG) to see if your heart is beating normally.