Serum Sodium Blood Test

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A serum sodium blood test is performed to measure the concentration of sodium within the blood. This test may be done for a number of reasons in addition to suspected abnormal sodium levels. This is a basic blood test and there is some preparation involved for some patients.

Why is this Test Performed?

If the patient is showing signs of a sodium imbalance this test may be performed. It may also be performed if the doctor suspects that the patient has a medical condition that may cause abnormal sodium levels. Many medical conditions and other factors may affect a patient’s sodium levels, including:

  • Recent surgery, shock, or trauma
  • Receiving sodium-containing intravenous fluids
  • Consuming small or large amounts of fluid or salt
  • Taking certain medications like the aldosterone hormone, or diuretics

Preparation and Procedure

Before a patient has a serum sodium blood test, his or her doctor will tell him or her what they need to do to prepare. Some drugs can increase the levels of sodium in the blood and may have to be temporarily discontinued if the doctor feels it is necessary. These include anabolic steroids, certain antibiotics, corticosteroids, lithium, birth control pills, clonidine, laxatives, and non-steroidal anti-inflammatory drugs.

Some drugs can decrease the levels of sodium in the blood and may have to be temporarily discontinued if the doctor feels it is necessary. These include carbamazepine, morphine, triamterene, diuretics, sulfonylureas, and vasopressin.

This test is a blood test and involves getting a blood sample so that it can be analyzed. A health care provider will either insert a needle into the patient’s vein, or with infants and young children, he or she will use a lancet. Some patients report moderate pain during the blood draw, but most report than this quick blood test is not painful.


If this test is deemed normal, the levels will range from about 135 to 145 mE/q/L, milliequivalents per liter. If the patient is determined to have too much sodium in their blood it may indicate:

  • The patient does not have enough fluid in their body, which may be due to fluid loss, such as diarrhea, burns, excessive sweating, or using diuretics
  • If the patient has high sodium levels, but normal water levels, it may be due to diabetes insipidus
  • If a patient has too much water in the body, it may be due to Cushing syndrome, hyperaldosteronism, or a diet high in sodium bicarbonate or salt

If the patient has too little sodium in their blood, it may indicate:

  • Low sodium and water levels may be due to vomiting, diarrhea, ketonuria, dehydration, or over diuresis
  • If sodium levels are low, but water levels are close to normal, it may indicate too much vasopressin hormone or SIADH
  • If sodium levels are low and water levels are high, it may indicate nephrotic syndrome, cirrhosis of the liver, congestive heart failure, or another kidney disease

This test may also be helpful for the following conditions:

  • Acute adrenal crisis
  • Drug-induced hypothyroidism
  • Hypopituitarism
  • Diabetic hyperglycemic hyperosmolar coma
  • Hepatorenal syndrome


University of California San Francisco Medical Center. (2009). Serum Sodium. Retrieved on November 25, 2010 from the University of California San Francisco Medical Center:

MedlinePlus. (2009). Sodium – Blood. Retrieved on November 25, 2010 from MedlinePlus: