What Does Potassium Level Mean on a Blood Test?

What it means

Potassium is an electrolyte that is mostly stored inside cells. The small amount in the blood matters a lot, because the heart, nerves and muscles need it in a steady range to send electrical signals. The kidneys are the main organ that keeps blood potassium balanced. Because large swings can affect the heart rhythm, labs often call the doctor directly when a result is very high or very low.

Potassium is on electrolyte panels and basic and comprehensive metabolic panels. Doctors check it often in people with kidney disease and in people taking medicines that can change it, such as diuretics, ACE inhibitors and angiotensin receptor blockers. A high level is called hyperkalemia; a low level is called hypokalemia.

A common reason for a falsely high potassium is a hemolyzed sample, where red cells burst in the tube and release their potassium. A long time with the tourniquet on, clenching the fist, or a delay before the sample reaches the lab can do the same. The lab may comment on this and ask for a repeat sample.

Where you may see it

• Electrolyte panels, listed as "K"
• Basic and comprehensive metabolic panels
• Lab comments such as "Hemolyzed sample: potassium may be falsely raised"