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Dilutional hyponatremia; Euvolemic hyponatremia; Hypervolemic hyponatremia; Hypovolemic hyponatremia

Hyponatremia is a condition in which the amount of sodium (salt) in the blood is lower than normal. 

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  • Causes

    Sodium is found mostly in the body fluids outside the cells. It is very important for maintaining blood pressure. Sodium is also needed for nerves, muscles, and other body tissues to work properly.

    When the amount of sodium in fluids outside cells drops, water moves into the cells to balance the levels. This causes the cells to swell with too much water. Brain cells are especially sensitive to swelling, and this causes many of the symptoms of hyponatremia.

    In hyponatremia, the imbalance of water to salt is caused by one of three conditions:

    • Euvolemic hyponatremia -- total body water increases, but the body's sodium content stays the same
    • Hypervolemic hyponatremia -- both sodium and water content in the body increase, but the water gain is greater
    • Hypovolemic hyponatremia -- water and sodium are both lost from the body, but the sodium loss is greater

    Hyponatremia can be caused by:

    • Burns that affect a large area of the body        
    • Diarrhea
    • Diuretic medicines, which increase urine output
    • Heart failure
    • Kidney diseases
    • Liver cirrhosis
    • Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
    • Sweating
    • Vomiting
  • Symptoms

    Common symptoms include:

    • Confusion
    • Convulsions
    • Fatigue
    • Headache
    • Irritability
    • Loss of appetite
    • Muscle spasms or cramps
    • Muscle weakness
    • Nausea
    • Restlessness
    • Vomiting
  • Exams and Tests

    The health care provider will perform a complete physical examination to help determine the cause of your symptoms. Blood and urine tests will be done.

    The following laboratory tests can confirm and help diagnose hyponatremia:

    • Comprehensive metabolic panel (includes blood sodium)
    • Osmolality blood test
    • Urine osmolality
    • Urine sodium
  • Treatment

    The cause of hyponatremia must be diagnosed and treated. If cancer is the cause of the condition, radiation, chemotherapy, or surgery to remove the tumor may correct the sodium imbalance.

    Other treatments depend on the specific type of hyponatremia.

    Treatments may include:

    • Fluids through a vein (IV)
    • Medication to relieve symptoms
    • Water restriction
  • Outlook (Prognosis)

    The outcome depends on the condition that is causing the problem. Acute hyponatremia, which occurs in less than 48 hours, is more dangerous than hyponatremia that develops slowly over time. When sodium level falls slowly over days or weeks (chronic hyponatremia), the brain cells have time to adjust and swelling is minimal.

  • Possible Complications

    In severe cases, hyponatremia can lead to:

    • Decreased consciousness, hallucinations or coma
    • Brain herniation
    • Death
  • When to Contact a Medical Professional

    Hyponatremia can be a life-threatening emergency. Call your health care provider right away if you have symptoms of this condition.

  • Prevention

    Treating the condition that is causing hyponatremia can help. If you play sports, drink fluids such as sports drinks that contain electrolytes. Drinking only water while you are active can lead to acute hyponatremia.

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Skorecki 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.


Review Date: 4/14/2013  

Reviewed 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 A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.

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