Sodium

Measured in mmol/L

The main electrolyte in the fluid outside your cells, reflecting the balance between water and salt in your body more than how much salt you eat.

What it is

Sodium is an electrolyte — a mineral that carries a tiny electrical charge and helps control how much water your body holds and how nerves and muscles fire. Your kidneys, hormones, and thirst work together to keep it in a narrow range, so it's usually read alongside the rest of the basic metabolic panel (potassium, chloride, CO2, kidney markers) rather than on its own. Because it mostly tracks water balance, a sodium value can shift with hydration, recent fluid loss, or certain medications, and small deviations from the reference range are common and often not meaningful by themselves.

Typical range

  • Adults135–145 mmol/L

Source · Mayo Clinic Laboratories (NAS) (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

  • Is my sodium result within the range you'd expect for me, or is it something worth watching?
  • Could my hydration, recent illness, or any medications I take be affecting this number?
  • Would it help to look at my sodium alongside my other electrolytes or repeat it at another visit?