Sodium blood test
The sodium blood test measures the amount of sodium in the blood.
Sodium can also be measured using a urine test.
Serum sodium; Sodium - serum
How the Test is Performed
A blood sample is needed.
How to Prepare for the Test
Your doctor may tell you to temporarily stop taking medicines that may affect the test. These include:
- Birth control pills
- High blood pressure medicines
- Nonsteroidal anti-inflammatory drugs (NSAIDs)
- Water pills (diuretics)
Do not stop taking any medicine before talking to your doctor.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. These soon go away.
Why the Test is Performed
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.
This test is usually done as part of an electrolyte or basic metabolic panel blood test.
Your blood sodium level represents a balance between the sodium and water in the food and drinks you consume and the amount in your 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 medicines, including the hormone aldosterone
The normal range for blood sodium levels is 135 to 145 milliequivalents per liter (mEq/L).
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.
Higher than normal sodium level is called hypernatremia. It may be due to:
- Adrenal gland problems such as Cushing syndrome or hyperaldosteronism
- Diabetes insipidus (type of diabetes in which kidneys are not able to conserve water)
- Increased fluid loss due to excessive sweating, diarrhea, use of diuretics, or burns
- Too much salt or sodium bicarbonate in the diet
- Use of certain medicines, including birth control pills, corticosteroids, laxatives, lithium, and NSAIDs such as ibuprofen or naproxen
Lower than normal sodium level is called hyponatremia. It may be due to:
- Adrenal glands not making enough of their hormones (Addison disease)
- Dehydration, vomiting, diarrhea
- Buildup in urine of waste product from fat breakdown (ketonuria)
- Increase in total body water seen in those with heart failure, certain kidney diseases, or cirrhosis of the liver
- Syndrome of inappropriate antidiuretic hormone secretion (antidiuretic hormone is released from an abnormal place in the body)
- Too much of the hormone vasopressin
- Use of medicines such as diuretics (water pills), morphine, and SSRI antidepressants
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:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Pincus MR, Abraham NZ Jr. Interpreting laboratory results. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 8.
Shorecki K, Ausiello D. Disorders of sodium and water homeostasis. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 118.
Last reviewed 10/29/2013 by 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, Bethanne Black, and the A.D.A.M. Editorial team.
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