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(Dilutional Hyponatremia; Euvolemic Hyponatremia; Hypervolemic Hyponatremia; Hypovolemic Hyponatremia)

Pronounced: hahy-po-nuh-TREE-mee-uh


Hyponatremia is a potentially serious condition in which the level of sodium in the blood is too low. An imbalance is created when there is too little sodium for the amount of water in the body. As a result, water moves into the body’s cells causing them to swell.

There are different types of hyponatremia, each resulting in low sodium in the blood:

  • Euvolemic hyponatremia—water level is low to normal, but the body is losing sodium
  • Hypervolemic hyponatremia—water and sodium may both be increased, but the water gain is greater
  • Hypovolemic hyponatremia—water and sodium decrease, but the sodium loss is greater

Causes    TOP

Hyponatremia may be caused by:

  • Syndrome of inappropriate antidiuretic hormone secretion (SIADH)—Antidiuretic hormone signals the kidneys to absorb more water, reducing urine output. In SIADH, the mechanism that stops antidiuretic hormone from collecting water is impaired. This impairment results in excess water in the body.
  • Sweating—In people with cystic fibrosis, excess sodium is excreted through sweat. It may also occur in people with severe burns when electrolytes and fluids are not replaced.
  • Some diuretics—Increased sodium is lost in the urine

Normal Anatomy of the Kidney

Kidney failure stones
Copyright © Nucleus Medical Media, Inc.

Risk Factors    TOP

Hyponatremia is more common in older adults. Other factors that may increase your chance of hyponatremia include:

  • Excess water intake without electrolytes—may occur when:
    • People are participating in endurance exercise
    • There is a lot of vomiting and/or diarrhea
  • Certain medications, such as some diuretics or antipsychotics
  • Certain health conditions, such as:
  • Having prostate surgery
  • Sweating in people without cystic fibrosis or severe burns

Symptoms    TOP

People with mild hyponatremia usually don't have symptoms. As hyponatremia progresses, symptoms will appear and worsen.

Moderate to severe hyponatremia may cause:

  • Nausea
  • Loss of appetite
  • Irritability
  • Headache
  • Restlessness
  • Sluggishness
  • Confusion
  • Hallucinations
  • Muscle twitching

Severe and rapid onset hyponatremia may cause seizures, coma, or death.

Diagnosis    TOP

You will be asked about your symptoms and medical history. A physical exam will be done. You will be asked about your fluid intake.

Tests may include:

  • Blood tests—to check the sodium level in your blood, and the functioning of your organs
  • Urine test—to check the sodium level in your urine

Other tests may be done to look for any underlying causes of your hyponatremia.

Treatment    TOP

Treatment may depend on:

  • What is causing the low sodium level
  • How long the sodium level has been low
  • How low the sodium level is
  • The level of hydration

In cases when the sodium has been low for more than 1-2 days, the doctor will want to correct the sodium level slowly. Serious complications may occur when sodium levels rise too rapidly. It can be corrected more quickly if it has been low for a short time.

Treatment options may include:

  • Restricting fluid intake if the amount of sodium is normal and there is too much fluid
  • IV fluids to deliver sodium and water to restore proper balance
  • Sodium may be given by mouth as sodium chloride (salt)
  • Identifying the underlying cause and getting proper treatment
  • Medications to help remove extra fluid from your body without losing more sodium

Prevention    TOP

To help reduce your chance of hyponatremia:

  • If participating in sports, drink only as much water as you need to quench your thirst. Sport drinks that provide electrolytes, such as sodium, along with water should be used during endurance events.
  • Work with your doctor to effectively manage any conditions that you may have.


American Society for Nutrition
National Institute of Diabetes and Digestive and Kidney Diseases


The College of Family Physicians of Canada


Elhassan EA, Schrier RW. Hyponatremia: Diagnosis, complications, and management including V2 receptor antagonists (vaptans). Curr Opin Nephrol Hypertens. 2011;20(2):161-168.
Hyponatremia. EBSCO DynaMed Plus website. Available at: Updated January 20, 2016. Accessed December 18, 2017.
Mittal R, Sheftel H, et al. Management of hyponatraemia. Br J Hosp Med (Lond). 2011;72(2):M22-5.
Syndrome of inappropriate antidiuresis (SIAD). EBSCO DynaMed website. Available at: http://www.dynamed.... Updated August 4, 2016. Accessed December 18, 2017.
Last reviewed December 2017 by EBSCO Medical Review Board Michael Woods, MD, FAAP
Last Updated: 12/20/2014

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