BLOOD TEST · SMART CARE POLYCLINIC, DEIRA
Sodium explained
The salt that governs body water balance — a measure of water, not of how much salt you eat.
What the Sodium test measures
The main salt in the fluid outside your cells. It determines how water is distributed through the body, and the kidneys hold it within a narrow range. A low sodium is usually about water balance rather than salt intake, and the European guideline treats finding the cause as the whole task.1
Reported as part of Kidney Function & Electrolytes.
What the result tells you
The thing most often misunderstood
A low sodium almost never means you need more salt. It means too much water for the sodium present, so the treatment is usually about water.
Common causes of a low result
Water tablets, some antidepressants, heart, liver or kidney disease, drinking large volumes quickly, and certain hormone problems.
Falling slowly versus quickly
A slow fall can be silent. A fast one causes nausea, headache, confusion and at the extreme seizures.
Why correction is deliberately slow
Raising sodium too quickly causes harm of its own, so it is corrected gradually and monitored.
If it's high
Nearly always water loss — not drinking enough, or losses through vomiting, diarrhoea or uncontrolled diabetes.
How to prepare
- Fasting
- Not needed
- Best time
- Any time, usually with the rest of the panel
- Worth knowing
- Drink normally beforehand. Both dehydration and a large volume of water shortly before shift the result.
What can move the result
A result outside the usual range does not on its own mean something is wrong. These are the everyday explanations a doctor considers first.
Frequently asked questions
The main salt in the fluid outside your cells. It determines how water is distributed through the body, and the kidneys hold it within a narrow range. A low sodium is usually about water balance rather than salt intake, and the European guideline treats finding the cause as the whole task. The thing most often misunderstood: A low sodium almost never means you need more salt. It means too much water for the sodium present, so the treatment is usually about water.
Fasting: Not needed. Best time: Any time, usually with the rest of the panel. Drink normally beforehand. Both dehydration and a large volume of water shortly before shift the result.
Commonly: water tablets and some antidepressants; how much water you drank before the test; vomiting, diarrhoea or heavy sweating; heart, liver or kidney disease; hormone conditions affecting water balance. A single result is not a diagnosis. Values are read against the laboratory's own reference range and alongside your history, your symptoms and the rest of the panel — which is why every package includes a doctor to go through them with you.
At Smart Care Polyclinic, 29 Doha Centre, Al Maktoum Rd, Deira, Dubai. Walk in during opening hours or call +971 (0)4 379 3562.
Sources
Written from current guidance and reviewed 31 August 2026.
Sources cited above
- Spasovski G, Vanholder R, Allolio B, Annane D, et al.. Clinical practice guideline on diagnosis and treatment of hyponatraemia. European Journal of Endocrinology. 2014;170(3):G1-47. PMID 24569125. doi:10.1530/EJE-13-1020The European guideline on low blood sodium — how it is investigated and why the cause matters more than the number.
Sources are listed for the specific statements they support. They are published research and guidance, not a substitute for a consultation — what applies to you is decided by a doctor who has assessed you.
- Sodium blood testMedlinePlus, US National Library of Medicine
- HyponatraemiaNHS
- ElectrolytesTesting.com, Association for Diagnostics & Laboratory Medicine