An Overview of Hyponatremia

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Sodium is an important electrolyte in the body that transmits electrical signals between cells and also helps keep fluid within cells. Too little sodium in the body—an electrolyte condition called hyponatremia—usually occurs as a result of the body failing to remove water normally. In other words, the body loses or holds onto too much water, which ultimately affects the body's sodium content.

Symptoms of hyponatremia, or low sodium in the body, may include nausea and vomiting, confusion, weakness, and in severe cases, seizures, coma, and even death.

In order to diagnose hyponatremia, a doctor will perform a medical history, physical examination, and order laboratory tests. Treatment involves addressing the underlying cause—such as administering a salt-water solution through the vein, or alternatively, restricting water and salt intake.


Hyponatremia is medically defined as a serum sodium level of less than 135 milliequivalents/liter (mEq/L).

A normal sodium level is between 135 and 145 mEq/L. Your sodium level can be measured within a simple blood test, called a basic or complete metabolic panel.

To understand the cause or the "why" behind a patient's hyponatremia, a doctor will first need to access a patient's volume status (the amount of water in their body).

From there, hyponatremia is generally broken down into three groups:

  • Hypovolemic Hyponatremia
  • Euvolemic Hyponatremia
  • Hypervolemic Hyponatremia

Hypovolemic Hyponatremia

Hypovolemic hyponatremia occurs when the body loses too much water with an even greater decrease in the sodium level.

Usually, the fluid loss is from the kidneys (for example, from overuse of a diuretic) or from the digestive tract (for example, from severe and/or persistent vomiting and/or diarrhea). Primary adrenal insufficiency (called Addison's disease) is another cause of hypovolemic hyponatremia.

Euvolemic Hyponatremia

Euvolemic hyponatremia occurs when the total amount of water in the body is increased, but the sodium level remains normal. This may happen with athletes who engage in intense exercises, like a marathon or triathlon, and then drink too much water, or in people who consume excess amounts of alcohol or use 3,4-methylenedioxymethamphetamine (“Ecstasy”).

Malnutrition, severe hypothyroidism, and a water-retaining condition called syndrome of inappropriate antidiuretic hormone secretion (SIADH) can also cause this type of hyponatremia.

Hypervolemic Hyponatremia

Hypervolemic hyponatremia occurs when the body holds on to too much water, relative to its sodium content.

Medical conditions that may cause this type of hyponatremia, include:


The symptoms of hyponatremia depend on the rate at which the sodium level dropped and the severity of the drop. In fact, many people with hyponatremia have no symptoms—instead, the electrolyte abnormality is found incidentally through a blood test drawn for other purposes.

Hyponatremia may cause a variety of potential symptoms including:

  • Weakness
  • Headache
  • Nausea and vomiting
  • Muscle cramps
  • Restlessness or irritability
  • Slurred speech
  • Confusion

Signs of volume overload (too much water) in the body, such as swelling (called edema) and/or ascites, are usually present in patients with hypervolemic hyponatremia. On the other hand, patients with hypovolemic hyponatremia have signs of dehydration from volume loss (e.g., dry mouth, decreased skin elasticity, and orthostatic hypotension).

In severe cases (when the sodium levels drop below 125 or 120 mEq per L), seizure and coma may occur, along with brain swelling, irreversible neurologic damage, and possibly, death.


The diagnosis of hyponatremia involves a medical history, physical examination, and various laboratory tests.

Medical History and Physical Examination

In addition to asking you pertinent questions that may suggest a diagnosis of hyponatremia and its underlying cause (e.g., diuretic use or history of severe vomiting or diarrhea), your doctor will perform a physical exam that includes a neurologic exam and an assessment of your volume status (e.g., whether edema or signs of dehydration are present).

Laboratory Tests

In addition, the following tests may be ordered to make a diagnosis of hyponatremia:

Other laboratory tests may be ordered to determine the cause of a person's hyponatremia, such as a thyroid-stimulating hormone (TSH) test, cortisol level, or adrenocorticotropic hormone (ACTH) stim test.


The treatment of hyponatremia is complex and varies, based on a number of factors, such as:

  • Presence or absence of symptoms
  • The severity of the sodium drop
  • Whether the hyponatremia is "acute" or "chronic."
  • Volume status of the patient (e.g., if there is a water deficit)
  • Underlying cause

For example, for hypervolemic hyponatremia from heart failure or cirrhosis, treatment usually includes restricting salt and water intake, as well as diuretic use, to rid the body of excess water.

On the other hand, for hypovolemic hyponatremia from severe vomiting or diarrhea, intravenous (through the vein) fluid administration with a salt-containing water solution is usually administered.

Other therapies may include:

  • Taking oral salt tabs or increasing salt in the diet
  • Discontinuing or cutting back on a medication causing the hyponatremia
  • Taking a medication called a vasopressin receptor antagonist (Vaptan)

A Word From Verywell

Hyponatremia is a common electrolyte condition that varies considerably in severity and etiology. Being knowledgeable of the potential symptoms and causes is a key first step to understanding this disorder. If you are concerned about your sodium level—perhaps, you saw the result on a routine blood test—be sure to discuss it with your doctor.

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