Sodium
The main electrolyte outside cells, reflecting the balance of salt and water in the body.
| Typical reference range | 135–146 mmol/L |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Sodium controls fluid distribution, blood pressure and nerve and muscle function. Blood sodium is regulated mostly through water balance via thirst, antidiuretic hormone (ADH) and the kidneys, with aldosterone controlling sodium excretion.
Why it matters
Abnormal sodium usually reflects a water balance problem rather than salt intake. Low sodium (hyponatremia) is the most common electrolyte disorder and can cause confusion, falls and seizures when severe.
What a high result can mean
High sodium usually indicates dehydration (inadequate water intake or excess water loss through sweating, diarrhea or diabetes insipidus).
What a low result can mean
Low sodium can result from excess water intake (including during endurance events), thiazide diuretics, SSRIs and other medications, SIADH, heart, liver or kidney failure, hypothyroidism, adrenal insufficiency, and severe vomiting or diarrhea.
What affects the result
Drinking large volumes of water before the draw can lower sodium slightly. Very high glucose or triglycerides can make sodium appear falsely low. Interpret with chloride, potassium, glucose and kidney markers.
Units and conversion
Usually reported in mmol/L.
- From mEq/L: multiply by 1 to get mmol/L
Also called on lab reports
Na, Sodium, Serum, Na+
Related tests: Electrolytes & Minerals
This page is educational and does not replace advice from a healthcare professional.