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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.
Other electrolytes, such as sodium, calcium, chloride, magnesium, and phosphate, may be checked in a blood sample at the same time as a blood test for potassium.
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
In general, there's nothing you have to do before this test, unless your doctor tells you to.
How It Is Done
A health professional uses a needle to take a blood sample, usually from the arm.
How It Feels
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
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 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, alcohol use disorder, 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.
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Current as of:
June 17, 2021
Author: Healthwise Staff
Adam Husney MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Martin J. Gabica MD - Family Medicine
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