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Sodium
The sodium concentration in blood. Counter-intuitively, it is mostly a measure of water balance rather than of salt intake: the body defends sodium concentration by moving water, so an abnormal sodium usually means too much or too little water relative to salt, not too much or too little salt on the food.
General information only — not a diagnosis, not treatment and not a substitute for your doctor. Reference ranges differ between laboratories, so the range printed on your own report is the one that counts, and only a clinician who knows your history can say what a result means for you. Never start, stop or change a medicine or supplement based on this page.
Usual adult reference range
The ranges below are typical adult reference intervals. Your own laboratory sets its own, printed next to your result, and that is the one to compare against.
| Group | SI units (mmol/L) | Conventional (mEq/L) |
|---|---|---|
| Typical adult reference interval | 135-145 | 135-145 |
Source: Typical adult reference interval published by clinical laboratories. · checked 2026-09-02
What a high result generally indicates
A raised sodium nearly always means water depletion — not enough drinking, or too much loss — and is most often seen in people who cannot easily get a drink themselves. It is corrected carefully and medically, because correcting it too fast is itself harmful.
What a low result generally indicates
A low sodium is one of the commonest abnormalities on a blood test. Causes include some diuretics and antidepressants, heart, liver and kidney disease, hormonal problems, and drinking very large volumes of water. Symptoms range from none at all to confusion, and both the cause and the speed of onset matter.
These are general patterns, not a diagnosis. Many things cause a high or low result, and the same figure means different things in different people. What yours means is a question for the doctor who ordered the test.
What affects this result
- Thiazide diuretics are a leading medicinal cause of low sodium.
- SSRIs and some other antidepressants can lower it, especially in older people.
- Vomiting, diarrhoea and heavy sweating shift it in either direction.
- Very large water intake during endurance events lowers it.
- Heart failure, liver cirrhosis and kidney disease all disturb it.
- Very high triglycerides or protein can cause a falsely low reading on some analysers.
Before the test
No fasting needed. A prolonged tourniquet or a clenched fist can distort electrolyte results.
Any preparation instruction that comes with your test slip overrides this general note — follow the one your clinician or laboratory gave you.
The one thing to take from this page
The range above is a typical interval for orientation. Your own laboratory's range, printed beside your result, is the one that applies to you — and a result is only meaningful alongside your symptoms, your history, your medicines and your other tests. That reading is a clinician's job. This page cannot diagnose anything, cannot tell you to change a medicine or a supplement, and is not a substitute for the person who ordered your test.
Frequently asked questions
What is the normal range for sodium?
A typical adult reference interval is 135–145 mmol/L, but laboratories differ — the range printed on your own report is the one to use. And a result inside or outside a range is only meaningful in context, which is your doctor's reading, not a web page's.
What does a high sodium mean?
A raised sodium nearly always means water depletion — not enough drinking, or too much loss — and is most often seen in people who cannot easily get a drink themselves. It is corrected carefully and medically, because correcting it too fast is itself harmful.
What does a low sodium mean?
A low sodium is one of the commonest abnormalities on a blood test. Causes include some diuretics and antidepressants, heart, liver and kidney disease, hormonal problems, and drinking very large volumes of water. Symptoms range from none at all to confusion, and both the cause and the speed of onset matter.
Other markers
Haemoglobin
Hb, HGB
Ferritin
Serum ferritin
Vitamin D (25-OH)
25-hydroxyvitamin D, calcidiol
HbA1c
Glycated haemoglobin, A1c
Fasting glucose
Fasting plasma glucose, FPG
Total cholesterol
TC
All markers and the checker · Symptoms and nutrients · Medicine interactions
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