Potassium test

Definition

This test measures the amount of potassium in 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.

See also: Aldosterone test

Alternative Names

Hypokalemia test; K+

How the test is performed

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:

  • Aminocaproic acid
  • Angiotensin receptor blockers
  • Antineoplastic drugs
  • ACE inhibitors
  • Certain diuretics, called potassium-sparing diuretics
  • Epinephrine
  • Heparin
  • Histamine
  • Isoniazid
  • Mannitol
  • Succinylcholine

Drugs that can decrease potassium measurements include:

  • Acetazolamide
  • Aminosalicylic acid
  • Amphotericin B
  • Carbenicillin
  • Cisplatin
  • Certain diuretics
  • Gentamicin
  • Insulin
  • Laxatives
  • Nafcillin
  • Penicillin G
  • Phenothiazines
  • Salicylates
  • 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.

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:

  • Addison's disease (rare)
  • Blood transfusion
  • Certain medications
  • Crushed tissue injury
  • Hyperkalemic periodic paralysis
  • Hypoaldosteronism (very rare)
  • Kidney failure
  • Metabolic or respiratory acidosis
  • Red blood cell destruction
  • Too much potassium in your diet

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

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

Additional conditions under which the test may be performed:

  • Acute adrenal crisis
  • Acute bilateral obstructive uropathy
  • Acute nephritic syndrome
  • Bulimia
  • Chronic kidney failure
  • Cushing's disease
  • Cushing syndrome caused by adrenal tumor
  • Cushing syndrome - exogenous
  • Cushing syndrome - ectopic
  • Diabetic ketoacidosis
  • Primary thrombocythemia
  • Renal tubular acidosis - distal
  • Rhabdomyolysis
  • Thyrotoxic periodic paralysis

What the risks are

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:

  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

Special considerations

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.

References

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.