Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at September 28, 2016

Hyponatremia is an electrolyte abnormality where a person does not have enough sodium in their system. This condition can be mild to severe, depending on how low the sodium level has gone.


Definition & Facts

Hyponatremia is seen sometimes in isolation and sometimes as a complication of other medical illnesses. These illnesses can be heart failure, liver failure, renal failure, or pneumonia. A person's normal sodium level is 135-145 mEq/L. Hyponatremia is considered to be a blood sodium measure of less than 135. The classification of the condition is as follows:

  • Mild 130-134 mmol/L
  • Moderate 125-129 mmol/L
  • Profound less than 125 mmol/L

Symptoms & Complaints

Signs and symptoms of hyponatremia include the following:

The severity of the symptoms depends on how low the patient's sodium level has gone. The neurological symptoms usually occur when the sodium in the blood is very low. When the sodium levels are very low, water can enter the brain cells and cause swelling. This can result in a rise of intracranial pressure.

Chronic hyponatremia can result in neurological impairments. This can cause gait abnormalities and can result in falls. Hyponatremia has also been associated with an elevated probability of osteoporosis and an increase in the likelihood of bone fractures.


Sodium has a crucial role in the functioning of the body. It is involved with maintaining blood pressure, supports the work of nerves and muscles, and regulates the body's fluid balance. A variety of conditions and lifestyle factors can result in the condition. These include:

The causes of the condition are grouped into those that occur with high fluid volume (hypervolemia), normal fluid volume, and low fluid volume (hypovolemia). A lack of sodium in the diet is rarely the cause of the condition. High volume hyponatremia occurs where both sodium and water content increase. The increase in sodium results in hypervolemia and the increase in water content to hyponatremia.

In normal volume hyponatremia, there is volume expansion in the body. In low volume hyponatremia, the hypovolemia comes about as a result of sodium loss. The hyponatremia is caused by a comparatively smaller loss in total body water. Long periods of exercise may result in exercise-associated hyponatremia. It is more common amongst long-distance runners.

Diagnosis & Tests

The doctor must investigate the past health of the patient (medical history and family history), take a physical examination, and take laboratory tests to determine the cause of the condition. A blood test with a serum sodium level of 135 mEq/L is diagnostic for the condition. The doctor will also assess the patient's reactions and focus.

Treatment & Therapy

The treatment of the condition depends on what the underlying cause is. It also depends on whether the person's blood volume is high, normal, or low. If the patient presents with seizure or coma, the first thing that needs to be done is to make certain that their respiratory airway is open. The doctor must make sure that the patient is breathing, has normal blood pressure, and pulse.

When the patient stabilizes, the treatment will depend on whether the condition is chronic or acute. Acute hyponatremia is the less common form of the condition. The goal of treatment is to get the sodium levels back to normal to prevent cerebral edema and brain death. For most patients, if they take in less fluid, the kidneys will fix the problem on their own. If the patient is in a coma or is having seizures, then intravenous sodium may need to be administered.

Chronic hyponatremia is the more common form of the condition. Treatment must proceed slowly. If the sodium level is corrected too rapidly, then it may result in a condition known as central pontine myelinolysis. This condition is where parts of the brain stem get damaged and cause stroke-like symptoms. For this reason, the sodium level must be returned very slowly. 

Prevention & Prophylaxis

Research has indicated that runners often develop the condition after prolonged exercise. Therefore, they should drink adequate amounts of fluid and replace sodium when they exercise. A person should not lose more than two percent of their body weight during exercise. This can help prevent dehydration and electrolyte imbalances.

People who exercise and drink too much water can get a problem with water intoxication and low blood sodium levels. One should not gain any weight due to water consumption when they exercise. Infants should not be given plain water very much because this can lead to hyponatremia and electrolyte imbalances.