Potassium test

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

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to swell with blood.

A needle is inserted into the vein, and the blood is collected in an airtight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

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
• Antineoplastic drugs
• ACE inhibitors
• Certain diuretics
• Epinephrine
• Heparin
• Histamine
• Isoniazid
• Mannitol
• Succinylcholine

Drugs that can decrease potassium measurements include:

• Acetazolamide
• Aminosalicylic acid
• Amphotericin B
• Carbenicillin
• Cisplatin
• Certain diuretics
• Insulin
• Laxatives
• 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

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.

This test is routinely done as part of an electrolyte level test.

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 cause increased heart muscle activity, which can lead to an irregular heartbeat. High levels cause decreased heart muscle activity. Either situation can lead to a heart attack in some cases.

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

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

• Addison's disease (rare)
• Blood transfusion
• Crushed tissue injury
• Hyperkalemic periodic paralysis
• Hypoaldosteronism (very rare)
• Kidney failure
• Metabolic or respiratory acidosis
• Red blood cell destruction

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

• Chronic diarrhea or use of laxatives
• Cushing syndrome (rare)
• Diuretics
• 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

Risks associated with venipuncture are slight:

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

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

If puncturing the vein is difficult, injury to the red blood cells may cause potassium to be released from them, causing a falsely high result.