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Potassium test

Definition

This test measures the amount of potassium in the fluid portion (serum) of the blood. Potassium (K+) helps nerves and muscles communicate. It also helps move nutrients into cells and waste products out of cells.

Potassium levels in the body are mainly controlled by the hormone aldosterone.

Alternative Names

Hypokalemia test; K+

How the test is performed

A blood sample is needed. Most of the time blood is drawn from a vein located on the inside of the elbow or the back of the hand.

How to prepare for the test

Many medicines can interfere with blood test results.

  • Your health care provider will tell you if you need to stop taking any medicines before you have this test.
  • Do not stop or change your medications without talking to your doctor first.

How the test will feel

You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.

Why the test is performed

This test is a regular 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.

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).

Sometimes, the potassium test may be done in persons who are having an attack of paralysis.

Normal Values

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.

What abnormal results mean

High levels of potassium (hyperkalemia) may be due to:

Low levels of potassium (hypokalemia) may be due to:

Special considerations

If it is hard to get the needle into the vein to take the blood sample, injury to the red blood cells may cause potassium to be released. This may cause a falsely high result.

References

Seifter JR. Potassium disorders. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 119.


Review Date: 5/5/2013
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.
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