Potassium Test

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Why is the Test Performed?

Potassium (K+) is the major positive ion within cells and is particularly important for maintaining the electric charge on the cell membrane. This charge allows nerves and muscles to communicate and is necessary for transporting nutrients into cells and waste products out of the cell. The concentration of potassium inside cells is about 30 times that in the blood and other fluids outside of cells.

Potassium levels are mainly controlled by the steroid hormone aldosterone. (For more information see the aldosterone test.) Aldosterone is secreted from the adrenal gland when levels of potassium increase. Aldosterone, in turn, causes the body to rid itself of the excess potassium.

Metabolic acidosis (for example, caused by uncontrolled diabetes) or alkalosis (for example, caused by excess vomiting) can affect blood potassium.

Small changes in the potassium concentration outside cells can have substantial effects on the activity of nerves and muscles. This is particularly true of heart muscle. Low levels of potassium cause increased activity (which can lead to an irregular heartbeat), whereas high levels cause decreased activity. Either situation can lead to cardiac arrest in some circumstances.

In normal people, taking potassium supplements or potassium-containing drugs is of no consequences, because the kidneys efficiently dispose of excess potassium.