Potassium

The main salt inside your cells, of which only a small amount circulates in the blood.

Heart rhythm depends on keeping it in a narrow band, which is why it is checked with almost every medication that affects the kidneys.

A high result is very often the sample rather than you: a tight tourniquet, a clenched fist, or a tube that sat too long all leak potassium out of cells. An unexpected high value is normally repeated before it counts.

Worth discussing a value outside the range that repeats on a clean sample.