Sodium is a substance that the body needs to work properly. Sodium is found in most foods. The most common form of sodium is sodium chloride, which is table salt.
A test can be done to see how much sodium is in your blood.
How the test is performed
A blood sample is needed. For information on how this is done, see: Venipuncture
How to prepare for the test
Many medicines can interfere with sodium blood test results. Your health care provider will tell you if you need to stop taking any medicines before you have this test. Do not stop or change your medications without talking to your doctor first.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Your blood sodium level represents a balance between the sodium and water in the food and drinks you consume and the amount in urine. A small amount is lost through stool and sweat.
Many things can affect this balance. Your doctor may order this test if you:
Have had a recent injury, surgery, or serious illness
Consume large or small amounts of salt or fluid
Receive intravenous (IV) fluids
Take diuretics (water pills) or certain other medications, including the hormone aldosterone
The normal range for blood sodium levels is 135 to 145 milliequivalents per liter (mEq/L).
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
Abnormal sodium levels can be due to many different conditions.
A higher than normal sodium level is called hypernatremia. It may be due to:
Increased fluid loss due to excessive sweating, diarrhea, use of diuretics, or burns
Too much salt or sodium bicarbonate in your diet
Use of certain medicines, including birth control pills, corticosteroids, laxatives, lithium, and NSAIDs such as ibuprofen or naproxen
A lower than normal sodium level is called hyponatremia. This may be due to:
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Shorecki K, Ausiello D. Disorders of sodium and water homeostasis. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 118.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.