Definition

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 body:

• Euvolemic hyponatremia—water level increases, but sodium level stays the same
• Hypervolemic hyponatremia—water and sodium levels increase, but the water gain is greater
• Hypovolemic hyponatremia—water and sodium levels decrease, but the sodium loss is greater

Causes

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—Increase sodium is lost in the urine.

Risk Factors

Factors that may increase your chance of hyponatremia include:

• Advanced age
• 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:
  • Kidney failure
  • Heart failure
  • Advanced liver disease— cirrhosis
  • Underactive thyroid gland— hypothyroidism
  • Inflammation of the pancreas— pancreatitis
  • Inflammation of the abdominal lining— peritonitis
  • Treatment for uncontrolled diabetes
  • Certain types of cancer
  • Meningitis
  • Head injury
• Having prostate surgery
• Sweating in people without cystic fibrosis or severe burns

Symptoms

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

Your doctor will ask about your symptoms and medical history. A physical exam will be done. Your doctor will ask you about your fluid intake and do some tests.

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

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
• Your level of hydration

In cases when the sodium has been low for more than 1-2 days, your 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 lw for a short time.

Treatment options may include:

• Restricting fluid intake
• Identifying the underlying cause and getting proper treatment
• Medications to help remove extra fluid from your body
• IV fluids to deliver sodium restore proper balance

Prevention

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 may be helpful during endurance events.
• Work with your doctor to effectively manage any conditions that you may have.

National Institute of Diabetes and Digestive and Kidney Diseases http://www.niddk.nih.gov

The College of Family Physicians of Canada http://www.cfpc.ca/ForPatients

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Hyponatremia. EBSCO DynaMed website. Available at:
http://www.ebscohost.com/dynamed
Updated July 9, 2014. Accessed November 6, 2014.

Mittal R, Sheftel H, et al. Management of hyponatraemia. Br J Hosp Med (Lond). 2011;72(2):M22-5.

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Updated December 15, 2012. Accessed November 15, 2013.