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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; Hyperkalemia 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 medicines without talking to your provider 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 part of a basic or comprehensive metabolic panel.

You may have this test to diagnose or monitor kidney disease. The most common cause of a high blood potassium level is kidney disease.

Potassium is important to heart function.

• Your provider 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 provider 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 people who are having an attack of paralysis.

Normal Results

The normal range is 3.7 to 5.2 milliequivalents per liter (mEq/L) 3.70 to 5.20 millimoles per liter (millimol/L).

Normal value ranges may vary slightly among different laboratories. Talk to your provider 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:

• Addison disease (rare)
• Blood transfusion
• Certain medicines, including angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), the potassium-sparing diuretics spironolactone, amiloride and triamterene, and beta adrenergic blockers
• Crushed tissue injury
• Hyperkalemic periodic paralysis
• Hypoaldosteronism (very rare)
• Kidney insufficiency or failure
• Metabolic or respiratory acidosis
• Red blood cell destruction
• Too much potassium in your diet

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

• Acute or chronic diarrhea
• Cushing syndrome (rare)
• Diuretics such as hydrochlorothiazide, furosemide, torsemide, and indapamide
• Hyperaldosteronism
• Hypokalemic periodic paralysis
• Not enough potassium in the diet
• Renal artery stenosis
• Renal tubular acidosis (rare)
• Vomiting

Risks

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

Mount DB. Disorders of potassium balance. In: Yu ASL, Chertow GM, Luyckx VA, Marsden PA, Skorecki K, Taal MW, eds. Brenner and Rector's The Kidney. 11th ed. Philadelphia, PA: Elsevier; 2020:chap 17.

Seifter JL. Potassium disorders. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 103.

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