The sodium blood test measures the concentration of sodium in the blood.
Sodium can also be measured using a
.
Your health care provider may tell you to temporarily stop taking medicines that may affect the test. These include:
Antibiotics
Antidepressants
Some high blood pressure medicines
Lithium
Nonsteroidal anti-inflammatory drugs (NSAIDs)
Water pills (diuretics)
Do not stop taking any medicine without talking to your provider.
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. This soon goes away.
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 provider may order this test if you:
Have had a recent injury, surgery, or serious illness
Consume usually large or small amounts of salt or fluid
Receive intravenous (IV) fluids
Take diuretics (water pills) or certain other medicines, including the steroid hormones such as hydrocortisone
The normal range for blood sodium levels is 135 to 145 milliequivalents per liter (mEq/L).
Normal value ranges may vary slightly among different labs. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.
An abnormal blood sodium level can be due to many different conditions.
Higher than normal blood sodium level is called hypernatremia. It may be due to:
Adrenal gland problems such as
or
(disorder in which the kidneys are not able to conserve water)
Increased fluid loss due to excessive sweating, diarrhea, or burns
Too much salt or sodium bicarbonate in the diet
Use of certain medicines, including corticosteroids, laxatives, lithium, and medicines such as ibuprofen or naproxen
Inadequate fluid intake, as is sometimes seen in people who are unable to recognize their thirst because of cognitive impairment or are unable to drink enough to keep up with their thirst because of difficulties accessing fluids
Lower than normal blood sodium level is called hyponatremia. It may be due to:
Adrenal glands not making enough of their hormones (
)
Buildup in urine of waste product from fat breakdown (ketonuria)
High blood sugar level (hyperglycemia)
High blood triglyceride lever (hypertriglyceridemia)
Increase in total body water seen in those with heart failure, certain kidney diseases, or cirrhosis of the liver
Increased fluid loss from body, vomiting, or diarrhea
Syndrome of inappropriate antidiuretic hormone secretion
(antidiuretic hormone is released in abnormal amounts or from an abnormal place in the body), causing the body to retain too much water
Too much of the hormone vasopressin
Underactive thyroid gland (hypothyroidism)
Use of medicines such as diuretics (water pills), morphine, and selective serotonin reuptake inhibitor (SSRI) antidepressants
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one person 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
Multiple punctures to locate veins
Fainting or feeling
(blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Serum sodium; Sodium - serum
Al-Awqati Q, Radhakrishnan J. Disorders of sodium and water. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 102.
Kashkouli A, Berl T, Sands JM. Disorders of water metabolism. In: Johnson RJ, Floege J, Tonelli M, eds. Comprehensive Clinical Nephrology. 7th ed. Philadelphia, PA: Elsevier; 2024:chap 9.
Kliegman RM, St. Geme JW, Blum NJ, et al. Electrolyte and acid-base disorders. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 73.
Oh MS, Briefel G, Pincus MR. Evaluation of renal function, water, electrolytes, and acid-base balance. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 15.
Updated by: Jacob Berman, MD, MPH, Associate Professor of Medicine, Division of General Internal Medicine, University of Washington School of Medicine, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.