A potassium test checks how much potassium is in the blood. Potassium is both an electrolyte and a mineral. It helps keep the water (the amount of fluid inside and outside the body's cells) and electrolyte balance of the body. Potassium is also important in how nerves and muscles work.
Potassium levels often change with sodium levels. When sodium levels go up, potassium levels go down, and when sodium levels go down, potassium levels go up. Potassium levels are also affected by a hormone called aldosterone, which is made by the adrenal glands.
Potassium levels can be affected by how the kidneys are working, the blood pH, the amount of potassium you eat, the hormone levels in your body, severe vomiting, and taking certain medicines, such as diuretics and potassium supplements. Certain cancer treatments that destroy cancer cells can also make potassium levels high.
Many foods are rich in potassium, including bananas, orange juice, spinach, and potatoes. A balanced diet has enough potassium for the body's needs. But if your potassium levels get low, it can take some time for your body to start holding on to potassium. In the meantime, potassium is still passed in the urine, so you may end up with very low levels of potassium in your body, which can be dangerous.
A potassium level that is too high or too low can be serious. Abnormal potassium levels may cause symptoms such as muscle cramps or weakness, nausea, diarrhea, frequent urination, dehydration, low blood pressure, confusion, irritability, paralysis, and changes in heart rhythm.
Why It Is Done
A blood test to check potassium is done to:
- Check levels in people being treated with medicines such as diuretics and for people having kidney dialysis.
- Check to see whether treatment for too low or too high potassium levels is working.
- Check people with high blood pressure who may have a problem with their kidneys or adrenal glands.
- Check the effects of extra nutrition (total parenteral nutrition [TPN]) on potassium levels.
- Check to see whether certain cancer treatments are causing too many cells to be destroyed (cell lysis). Cell lysis syndrome causes very high levels of some electrolytes, including potassium.
How To Prepare
You do not need to do anything before having this test.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).
How It Is Done
The health professional drawing blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure on the site and then put on a bandage.
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having blood sample taken from a vein.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
- Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (such as Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.
A potassium test checks how much potassium is in the blood. Potassium is an electrolyte and mineral.
The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Blood potassium levels also vary with age.
Results are ready in 1 day.
3.4-4.7 mEq/L or 3.4-4.7 mmol/L
4.1-5.3 mEq/L or 4.1-5.3 mmol/L
3.7-5.9 mEq/L or 3.7-5.9 mmol/L
Many conditions can affect potassium levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.
- High blood potassium levels may be caused by damage or injury to the kidneys. This prevents the kidneys from removing potassium from the blood normally.
- High blood potassium levels can also be caused by conditions that move potassium from the body's cells into the blood. These conditions include severe burns, crushing injuries, heart attack, and diabetic ketoacidosis.
- Taking too many potassium supplements can also cause high levels of potassium in the blood.
- Too much acid (pH) in the blood makes potassium levels higher by causing the potassium in the body's cells to "leak" out of cells and into the blood.
- Some medicines, such as aldosterone antagonists and angiotensin-converting enzyme (ACE) inhibitors, can cause high potassium levels.
- Low blood potassium levels can be caused by high levels of aldosterone (hyperaldosteronism) made by the adrenal glands.
- Other conditions that can cause low blood potassium levels include severe burns, cystic fibrosis, alcoholism, Cushing's syndrome, dehydration, malnutrition, vomiting, diarrhea and certain kidney diseases, such as Bartter's syndrome. Bartter's syndrome is a condition characterized by enlargement of certain kidney cells. It is more common in children and may be linked to an abnormally short stature (dwarfism). The cause of Bartter's syndrome is not fully known.
- Medicines, such as diuretics, are a common cause of low potassium levels.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- Destruction of the red blood cells in the blood sample, which can happen when blood is taken or when it is being processed in the lab. When red blood cells are broken up, they release large amounts of potassium and can cause false high values.
- Taking potassium supplements.
- Taking medicines, such as antibiotics that contain potassium (such as a type of penicillin g), nonsteroidal anti-inflammatory drugs (NSAIDs), heparin, insulin, glucose, corticosteroids, diuretics, medicines used to treat high blood pressure and heart disease, and natural licorice (Glycyrrhiza glabra).
- The overuse of laxatives.
- Severe vomiting.
What To Think About
- Low blood potassium values are more common than high blood potassium values.
- An electrocardiogram (EKG or ECG) may show signs of a very high or very low blood potassium level because of the effect potassium has on the heart. To learn more, see the topic Electrocardiogram.
- Other electrolyte tests, such as sodium, calcium, chloride, magnesium, phosphate, blood urea nitrogen (BUN), and creatinine, are often done at the same time as a test for potassium.
To learn more, see:
- Sodium (Na) in Blood.
- Calcium (Ca) in Blood.
- Chloride (Cl).
- Magnesium (Mg).
- Blood Urea Nitrogen.
- Creatinine and Creatinine Clearance.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Primary Medical ReviewerAdam Husney, MD - Family Medicine
E. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerAvery L. Seifert, MD - Urology
Current as ofNovember 2, 2015