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Low Blood Sodium (Hyponatremia)

What does it mean to have low blood sodium?

Sodium is an essential electrolyte that helps maintain the balance of water in and around your cells. It’s important for proper muscle and nerve function. It also helps maintain stable blood pressure levels.

Insufficient sodium in your blood is also known as hyponatremia. It occurs when water and sodium are out of balance. In other words, there’s either too much water or not enough sodium in your blood.

Normally, your sodium level should be between 135 and 145 milliequivalents per liter (mEq/L). Hyponatremia occurs when your sodium level goes below 135 mEq/L.

Symptoms of low sodium in blood

Symptoms of low blood sodium can vary from person to person. If your sodium levels fall gradually, you may not experience any symptoms. If they drop very quickly, your symptoms may be more severe.

Losing sodium quickly is a medical emergency. It can cause loss of consciousness, seizures, and coma.

Common symptoms of low blood sodium include:

Causes of low sodium in blood

Many factors can cause low blood sodium. Your sodium levels may get too low if your body loses too much water and electrolytes. Hyponatremia may also be a symptom of certain medical conditions.

Causes of low sodium include:

Who is at risk for low sodium in blood?

Certain factors increase your risk of low blood sodium, including:

  • old age
  • diuretic use
  • antidepressant use
  • being a high-performance athlete
  • living in a warmer climate
  • eating a low-sodium diet
  • having heart failure, kidney disease, syndrome of inappropriate anti-diuretic hormone (SIADH), or other conditions

If you’re at risk for low sodium, you may need to be more careful about your intake of electrolytes and water.

Tests for low sodium in blood

A blood test can help your doctor check for low sodium levels. Even if you don’t have symptoms of low blood sodium, your doctor may order a basic metabolic panel. This tests the amounts of electrolytes and minerals in your blood. A basic metabolic panel is often part of a routine physical. It may identify low blood sodium in someone without any symptoms.

If your levels are abnormal, your doctor will order a urine test to check the amount of sodium in your urine. The results of this test will help your doctor determine the cause of your low blood sodium:

  • If your blood sodium levels are low but your urine sodium levels are high, your body is losing too much sodium.
  • Low sodium levels in both your blood and your urine mean your body is not taking in enough sodium. There may also be too much water in your body.

Treatment for low blood sodium

Treatment for low blood sodium varies depending on the cause. It may include:

  • cutting back on fluid intake
  • adjusting the dosage of diuretics
  • taking medications for symptoms such as headaches, nausea, and seizures
  • treating underlying conditions
  • infusing an intravenous (IV) sodium solution

Prevention of low blood sodium

Keeping your water and electrolyte levels in balance can help prevent low blood sodium.

If you’re an athlete, it’s important to drink the right amount of water during exercise. You should also consider drinking a rehydration beverage, such as Gatorade or Powerade. These drinks contain electrolytes, including sodium. They help replenish sodium lost through sweating. These drinks are also helpful if you lose a lot of fluids through vomiting or diarrhea.

During a typical day, women should aim to drink 2.2 liters of fluids. Men should aim for 3 liters. When you’re adequately hydrated, your urine will be pale yellow or clear and you won’t feel thirsty.

It’s important to increase your fluid intake if:

  • the weather is warm
  • you’re at a high altitude
  • you’re pregnant or breastfeeding
  • you’re vomiting
  • you have diarrhea
  • you have a fever

You should drink no more than 1 liter of water per hour. Don’t forget that it’s possible to drink too much water too quickly.

Other electrolyte disorders: Hypernatremia

Hypernatremia is rare. It occurs when a person does not get enough water because of either limited access to water or an impaired thirst mechanism. It’s caused less commonly by diabetes insipidus. It occurs when your serum sodium level exceeds 145 mEq/L.

Hypernatremia can cause:

Content licensed from:

Written by: Janelle Martel
Medically reviewed on: Mar 28, 2017: Steven Kim, MD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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