What is sodium?

Sodium is an electrolyte that is present in all body fluids.  The highest concentration is found in the blood.  Sodium is essential for normal body function and, along with potassium and calcium, helps cells to work properly and to regulate the amount of fluid in the body.

Sodium is essential for a number of body functions, including muscle and nerve function. Most people get sufficient (or excess) dietary sodium from the foods they eat. The body tries to keep blood sodium levels strictly balanced with the help of mechanisms including hormonal regulation that prevents dehydration and triggering thirst if sodium levels are slightly low.

A sodium blood test measures the level of sodium in the blood.  This test can help to evaluate electrolyte balance and determine whether your sodium is within normal limits.  Urine levels should also be considered.

Why test sodium?

Unless this is ordered as a retest or for a specific reason, we recommend ordering this as part of a health test.

Health check
Discover your risk factors for lifestyle diseases in time to do something about them.

Lifestyle factors
You drink a lot of alcohol and/or eat a diet low in nutrient-rich foods like fruits, vegetables, nuts, seeds and beans and high in processed foods and sodium.

Monitor changes to your blood values as you make lifestyle changes, and take supplements or medication.

You are suffering from dehydration, high blood pressure, or edema.

Maintaining the correct balance of electrolytes in your blood is crucial to performance.

What causes low sodium?
Hyponatremia can have many different causes. The most common cause of low sodium in otherwise healthy people is sodium loss (for example diarrhea, excessive sweating, use of diuretics, edema, endurance exercise, adrenal problems, excess water intake, and certain medications).

Low sodium levels are more common in the elderly. Serious health conditions associated with low sodium include heart failure, liver cirrhosis, kidney damage, and blood loss.

What causes high sodium?

Known as hypernatremia, a high blood sodium level is nearly always caused by dehydration (not replacing lost water with sufficient water. Rarely, it is caused by increasing salt intake without enough water.

Other reasons include Cushing syndrome and a condition caused by too little ADH called diabetes insipidus. Urine levels should also be considered. There are a number of reasons for decreased urinary sodium including dehydration, and heart, kidney, and liver problems.

More information

Some drugs can increase sodium levels. These include anabolic steroids, antibiotics, corticosteroids, laxatives, cough medicines, and oral contraceptives.

Drugs that can decrease sodium levels include ACE inhibitors, diuretics, carbamazepine, heparin, and tricyclic antidepressants.


No advance preparation is needed for this test.

On the day of the test

Remember to take I.D. with you when going to take a test.

Arrive early and sit down quietly for 15 minutes before the test is taken.


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