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.