Proceeds from website advertising help sustain Lab Tests Online. AACC is a not-for-profit organization and does not endorse non-AACC products and services.


Print this article
Share this page:
Also known as: Na
Formal name: Sodium

The Test Sample

What is being tested?

This test measures the level of sodium in the blood. Sodium is an electrolyte that is vital to normal body processes, including nerve and muscle function. Sodium, along with other electrolytes such as potassium, chloride, and bicarbonate (or total CO2), helps cells function normally and helps regulate the amount of fluid in the body. Sodium is present in all body fluids but is found in the highest concentration in the blood and in the fluid outside of the body’s cells. This extracellular sodium, as well as all body water, is regulated by the kidney.

We get sodium in our diet, from table salt (sodium chloride or NaCl), and to some degree from most of the foods that we eat. Most people have an adequate intake of sodium. The body uses what it requires and the kidneys excrete the rest in the urine to maintain the sodium concentration in blood within a very narrow range. It does this by:

  • Producing hormones that can increase (natriuretic peptides) or decrease (aldosterone) sodium losses in urine 
  • Producing a hormone that prevents water losses (antidiuretic hormone, ADH)
  • 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 control systems. When the level of sodium in the blood changes, the water content in the body also changes. These changes can be associated with dehydration or edema, especially in the legs.

How is the sample collected for testing?

A blood sample is taken by needle from the arm. In some cases, a 24-hour urine sample may be required.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

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

No test preparation is needed.