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.

Where you can get this tested

Sodium is included in the following WMG Health panels. Same-day appointments at our Harley Street clinic, with results clinician-reviewed.

General Wellness
£279
View panel

Want a specific combination of markers we do not have a panel for? Build a custom panel and our clinicians will design one for you.

Looking to book a test?

Comprehensive private health screening

Full blood screening at 134 Harley Street, London, reviewed by GMC-registered doctors with a written interpretation.

View the panel → 020 3239 3378

Symptoms often investigated with Sodium

Sodium is commonly tested when patients present with the following symptoms. If any of these resonate with you, the linked guides explain what to look for and which test pathway is appropriate.

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Related markers

Potassium Urea Creatinine Uric acid Calcium

Browse all 50 markers in the biomarker library →

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 in several standard panels and as part of a custom panel at our 134 Harley Street clinic. Results are released as each marker is reviewed, and the completion date is set by the slowest marker in your panel. We confirm the expected timeframe at booking. Book a standard panel online, or ask for a custom panel via /contact/ or 020 3239 3378.