Potassium

Measured in mmol/L

An electrolyte central to heart and muscle signaling, kept in a tight range — and one where the blood draw itself can nudge the result.

What it is

Potassium is an electrolyte that lives mostly inside your cells and is essential for steady heart rhythm and muscle function. Your kidneys do most of the work keeping it in a narrow band, so it's reviewed as part of a panel with sodium, chloride, CO2, and kidney markers rather than in isolation. One honest caveat: if red blood cells break open during or after the draw (called hemolysis), or if you clenched your fist a lot during the blood test, potassium can read falsely high — so an unexpected result is often rechecked before it's taken at face value.

Typical range

  • Adults3.6–5.2 mmol/L

Source · Mayo Clinic Laboratories (KS) (2026)

Reference ranges vary between laboratories, and what is normal for you depends on your own history. Your own lab’s range is the one printed on your report.

Worth asking your clinician

  • Does my potassium result look meaningful to you, or could the sample or draw have affected it?
  • Do any of my medications or health conditions tend to move potassium up or down?
  • Would you want to repeat this test to confirm the value before we read anything into it?