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Also known as: Na
Formal name: Sodium

At a Glance

Why Get Tested?

To determine the cause of and monitor treatment for illnesses associated with abnormal sodium levels in the body

When to Get Tested?

If you are experiencing dehydration, oedema, problems with blood pressure, or have non-specific symptoms; or as part of routine laboratory evaluations

Sample Required?

A blood sample drawn from a vein in the arm or, in some cases, a urine sample

Test Preparation Needed?


The Test Sample

What is being tested?

This test measures the level of sodium in blood. Sodium is an electrolyte present in all body fluids and is vital to normal body function. It works to regulate the amount of water in the body, and to control blood pressure by keeping the right amount of water available (in some people, too much sodium from salt in the diet can contribute to high blood pressure). Your body tries to keep your blood sodium within a very small concentration range; it does so by:

  • producing hormones that can increase (such as natriuretic peptides) or decrease (such as aldosterone) sodium losses in urine
  • producing a hormone that prevents water losses (antidiuretic hormone [ADH], sometimes called vasopressin)
  • controlling thirst (even a 1% increase in blood sodium will make you thirsty and cause you to drink water, returning your sodium level to normal.)

Abnormal blood sodium is usually due to some problem with one of these systems. When the level of sodium in the blood changes, the water content in your body changes. These changes can be associated with dehydration (too little fluid) or oedema (too much fluid, often resulting in swelling in the legs).

How is the sample collected for testing?

A blood sample is taken by needle from the arm. In some cases, a urine sample may be required.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

Common Questions

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.