Hypernatremia: What It Is and What You Should Know

Medically Reviewed By Megan Soliman, MD
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Hypernatremia is when the sodium level in the blood is too high. Sodium is an essential electrolyte for the human body. However, having very high or very low levels of sodium in the body can be dangerous. Electrolytes help regulate the flow of nutrients and other products into and out of cells.

Sodium is familiar to many people as a component of table salt, or sodium chloride. However, it has an important role in the body in maintaining cellular health.

When blood sodium levels become too high, it can disturb the balance and function of the cells.

This article explains hypernatremia, including its causes, symptoms, and treatment options.

What is hypernatremia?

A person holds a clear plastic water bottle up to their lips to take a sip.
CAILIN HILL ARAKI/Getty Images

Having a high sodium level means that the ratio of water to sodium in the body is not at a typical level.

Doctors define hypernatremia as a blood sodium level higher than 145 milliequivalents per liter (mEq/l).

Sodium is an important electrolyte of the blood vessels, which make up the network of veins, arteries, and capillaries through which blood moves around the body. Sodium keeps water in the blood vessels so that you have enough blood volume.

Normally, the body regulates its sodium level by first regulating the levels of water in the body. By stimulating thirst and controlling the release of a hormone called vasopressin, or antidiuretic hormone (ADH), the body can control how much water and sodium the kidneys absorb.

Hypernatremia occurs when certain factors unbalance the levels of sodium and water.

Types of hypernatremia

There are different types of hypernatremia, and they vary according to the water balance in the body.

Your body keeps most of its water inside cells. This is intracellular fluid (ICF). Any remaining water is outside the cells in the blood vessels or in the spaces between cells. This is extracellular fluid (ECF).

The amounts of fluid present and where the fluid is located in the body determine the type of hypernatremia, as follows:

  • Hypovolemic hypernatremia: Hypovolemic hypernatremia is when there is not enough fluid volume in the blood vessels, which is part of the ECF. With this type of hypernatremia, your body loses more water than sodium. This causes the remaining ECF to have a higher concentration of sodium. Diuretics, or “water pills,” and diarrhea can cause this.
  • Euvolemic hypernatremia: This occurs when there is a typical amount of fluid volume in the blood, but the body is losing water from inside the cells. Diabetes insipidus, or a lack of thirst or access to water, can cause this type.
  • Hypervolemic hypernatremia: Hypervolemic hypernatremia means that there is too much fluid in the blood. This is rare, and it results from taking in too much sodium relative to water, or when the body holds on to too much sodium compared with water. This high amount of sodium causes water to diffuse into the blood, resulting in a high blood volume.

Hypernatremia vs. hyponatremia

Hyponatremia occurs when a person does not have enough sodium in the blood.

The typical range for blood sodium is 135–145 mEq/l. Hyponatremia is a level below 135 mEq/l. It can develop if you lose too much sodium in your urine or if there is too much fluid in the body.

Learn more about low sodium and hyponatremia.

Signs and symptoms

One main symptom of hypernatremia is thirst. However, some people may not have this symptom. In these cases, hypernatremia may be the result of an impaired sense of thirst.

Other symptoms are also neurologic, meaning that they affect the functioning of the brain and nervous system. They can include:

  • symptoms of dehydration, including:
    • feeling thirsty
    • dark yellow or strong smelling urine
    • infrequent urination, or urinating fewer than four times per day
    • dry mouth, lips, or eyes
    • extreme sleepiness, lethargy, or fatigue
    • dizziness or lightheadedness
    • not having urinated all day
    • a weak or rapid pulse
  • hyperactive reflexes
  • irritability or agitation

Symptoms may also include excessive thirst and urination if diabetes insipidus is the cause.

When to seek medical care

Hypernatremia and dehydration can cause some symptoms that are serious. Seek immediate medical care for severe symptoms, such as:

  • symptoms of dehydration
  • symptoms of dehydration in infants, which can also include:
    • unexpected drowsiness
    • rapid breathing
    • few tears when crying
    • a soft spot on their head that appears to sink inward
    • a dry mouth
    • dark yellow urine or infrequent urination
    • cold or blotchy looking hands and feet
  • difficulty communicating
  • confusion
  • seizures
  • coma or changes in consciousness

Causes

Hypernatremia often occurs when a person does not take in enough water, loses water from the body, or takes in too much sodium. Causes of this can include:

  • adrenal tumors
  • burns, which result in water loss through the skin
  • diarrhea or vomiting
  • excessive sweating
  • extremely rapid breathing, resulting in water loss through the lungs
  • fever
  • excessive sodium intake, such as by swallowing large amounts of seawater or as a result of certain medical treatments, including tube feedings
  • impaired or absent thirst
  • not drinking enough water, having a lack of access to water, or having a lack of ability to communicate the need for water
  • diuretic medications, or “water pills,” which rid the body of fluid and sodium
  • kidney disease
  • diabetes insipidus, including:
    • central diabetes insipidus, as it can cause a lack of ADH
    • nephrogenic diabetes insipidus, which does not affect ADH production but can reduce the response from the kidneys

People may take diuretic medications to treat conditions such as edema and high blood pressure.

Risk factors

Those who are at risk of experiencing dehydration may be at higher risk of developing hypernatremia.

Some researchers outline that the condition is more common among infants and older adults.

Those at particular risk may also include:

  • infants who experience gastroenteritis or ineffective breastfeeding
  • premature infants
  • people with a neurological disability that affects their thirst mechanisms
  • people who depend on others for access to water, such as those who cannot drink independently
  • those who receive hypertonic fluid infusions

Prevention

It is not always possible to prevent hypernatremia.

However, maintaining an appropriate water intake is one step you can take to reduce the risk of the condition.

To replace the fluid lost on a daily basis through typical activities, the average adult needs 1 to 1.5 liters of fluids per day. The exact amount may vary depending on how much water you lose through sweat, such as due to heat or exercise.

Drinks should primarily be water.

The following table outlines how much fluid children should drink per day.

Age of childRecommended fluid intake per day
1–3 years1 liter
4–8 years1.2 liters
9 years or older1.5 liters

Diagnosis

Doctors can diagnose hypernatremia using a blood chemistry or metabolic panel. This test measures various electrolytes, including sodium. If a sodium level comes back high, more testing may be necessary to determine the cause.

Doctors may also order urine tests and other blood tests to help with the diagnosis.

For diabetes insipidus-related hypernatremia, testing may involve a water deprivation test along with the drug desmopressin.

Treatment

Treating hypernatremia involves correcting both the sodium level and fluid level. The treatment to do this will depend on the underlying cause. Doctors will use formulas to calculate how much fluid to give.  

If you are conscious and not vomiting, doctors may be able to achieve fluid replacement orally. For those who are not conscious and those who are unable to keep water in their digestive tract, IV fluid administration is necessary. This involves using a small needle to connect a tube of fluid to a vein.

If the hypernatremia started within the previous 24-hour period, this treatment can usually take place over the following 24 hours. For chronic hypernatremia that has lasted longer or that has an unknown duration, the treatment can take 2 days or more, depending on the cause and whether or not you experience any additional conditions.

Frequent monitoring of electrolyte levels is necessary throughout the process.

Complications

Not all cases of hypernatremia will lead to complications. However, in severe cases, some complications can be serious.

Severe cases of hypernatremia can be fatal or cause brain damage. This may happen if the blood vessels rupture, cause a hemorrhage, or form blood clots.

Correcting hypernatremia too quickly can also cause complications. Rapid correction can cause too much water to move into cells. When this happens in the brain, it causes brain swelling. The brain cannot expand because the skull prevents it. The result is pressure on the brain, which can cause seizures, permanent brain damage, and death.

Outlook 

The outlook for people with hypernatremia depends on the underlying cause and the severity of the condition.

The key to effective treatment is correcting the fluid balance at the right rate. Those at high risk of developing hypernatremia again may need periodic monitoring.

Summary

Hypernatremia occurs when the level of sodium in the blood is too high. It occurs when something disrupts the body’s fluid and sodium balance. This can be the result of the body not taking in enough water, losing water, or not being able to regulate fluid and sodium levels.

People at particular risk of hypernatremia include infants and older adults, as well as anyone who may have difficulty accessing water themselves.

Treatment involves correcting the fluid balance by replacing it slowly over the course of a day or two. Complications of untreated hypernatremia can be serious.

Seek immediate medical help for any symptoms of moderate to severe dehydration, including excessive thirst, dark urine, and confusion.

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Medical Reviewer: Megan Soliman, MD
Last Review Date: 2022 Jun 30
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