Biomarker . Patient guide
Sodium Blood Test
What is Sodium
Sodium is the main electrolyte in the fluid outside your cells and is central to fluid balance, nerve signalling and blood pressure. It is measured as part of a U&E and is tightly controlled by the kidneys and hormones.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in mmol/L. Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Adults | 135 to 145 | mmol/L |
What it is
The body keeps blood sodium within a narrow range using thirst, the kidneys and hormones such as ADH and aldosterone. Because sodium and water move together, an abnormal sodium usually reflects a problem with water balance rather than salt intake itself.
Why a clinician would order it
Sodium is checked to investigate confusion, fatigue, dizziness or fluid problems, to monitor diuretics and other medicines, and as part of a routine U&E and health screen.
If your level is outside the range
Symptoms of low Sodium
- Nausea
- Headache
- Confusion or poor concentration
- Fatigue
- In severe cases: drowsiness, seizures
What low can indicate. Low sodium (hyponatraemia) is common and can result from certain medicines (diuretics, some antidepressants), drinking too much water, SIADH, heart, liver or kidney conditions, and hormone problems. It is one of the commonest electrolyte abnormalities.
Symptoms of high Sodium
- Thirst
- Dry mouth
- Lethargy
- Irritability
What high can indicate. High sodium (hypernatraemia) usually reflects water loss or inadequate water intake (dehydration), and less commonly hormone problems affecting water balance.
Testing tips
No fasting needed. A prolonged tourniquet or a difficult draw can affect electrolyte results, so a markedly abnormal value is often repeated.
Related markers
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.
Common questions about Sodium
What is a normal Sodium range?
Adults: 135 to 145 (mmol/L). Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low Sodium result mean?
Low sodium (hyponatraemia) is common and can result from certain medicines (diuretics, some antidepressants), drinking too much water, SIADH, heart, liver or kidney conditions, and hormone problems. It is one of the commonest electrolyte abnormalities.
What does a high Sodium result mean?
High sodium (hypernatraemia) usually reflects water loss or inadequate water intake (dehydration), and less commonly hormone problems affecting water balance.
Do I need to fast or prepare for the Sodium blood test?
No fasting needed. A prolonged tourniquet or a difficult draw can affect electrolyte results, so a markedly abnormal value is often repeated.
Can I order a Sodium blood test privately in London?
Yes. WMG Health offers Sodium as part of bespoke panels and several pre-built panels at our 134 Harley Street clinic. Results are clinician-reviewed by a GMC-registered doctor within 4 hours for the most common assays. All panels are custom-built around your specific question; bookings via /contact/ or 020 3239 3378.