A blood sample is needed. For information on how this is done, see: Venipuncture
How to prepare for the test
The health care provider may tell you to stop taking any drugs that may affect the test.
Drugs that can increase potassium measurements include:
Angiotensin receptor blockers
Certain diuretics, called potassium-sparing diuretics
Drugs that can decrease potassium measurements include:
Sodium polystyrene sulfonate
The following factors can interfere with the test:
Infusion of potassium-containing fluids
Infusion of glucose or insulin
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
This test is routinely done as part of a basic or comprehensive metabolic panel.
Your doctor may order this test to diagnose or monitor kidney disease. The most common cause of high potassium levels is kidney disease.
Because potassium is important to heart function, your doctor may order this test if you have signs of high blood pressure or heart problems. Small changes in potassium levels can have a big effect on the activity of nerves and muscles, especially the heart. Low levels of potassium can lead to an irregular heartbeat or other electrical malfunction of the heart. High levels cause decreased heart muscle activity. Either situation can lead to life-threatening heart problems.
It may also be done if your doctor suspects metabolic acidosis (for example, caused by uncontrolled diabetes) or alkalosis (for example, caused by excess vomiting).
Occasionally, the potassium test may be done in persons who are having an attack of paralysis.
The normal range is 3.7 to 5.2 mEq/L.
Note: mEq/L = milliequivalent per liter
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
If it is difficult to get the needle into the vein to take the blood sample, injury to the red blood cells may cause potassium to be released, causing a falsely high result.
Mount DB, Zandi-Nejad K. Disorders of potassium balance. In: Brenner BM, eds. Brenner and Rector’s The Kidney. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 15.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.