- Introduction
- What is hyponatremia (low blood sodium)?
- Types
- What are the types of hyponatremia?
- Causes
- What causes hyponatremia?
- Symptoms
- What are the warning signs of hyponatremia?
- Diagnosis
- Diagnosis of hyponatremia
- Treatment
- What is the treatment for hyponatremia?
What is hyponatremia (low blood sodium)?
Hyponatremia is low blood sodium or salt deficiency.
Hyponatremia refers to a lower-than-normal level of sodium in the blood. Sodium is essential for many body functions including the maintenance of fluid balance, regulation of blood pressure, and normal function of the nervous system. Hyponatremia has sometimes been referred to as "water intoxication," especially when it is due to the consumption of excess water, for example during strenuous exercise, without adequate replacement of sodium.
Sodium is the major positively charged ion (cation) in the fluid outside of cells of the body. The chemical notation for sodium is Na. When combined with chloride (Cl), the resulting substance is table salt (NaCl).
The normal blood sodium level is 135 - 145 milliEquivalents/liter (mEq/L), or in international units, 135 - 145 millimoles/liter (mmol/L). Normal range (the levels identified by a laboratory as normal) may vary slightly among different laboratories.
What are the types of hyponatremia?
The three most common ways to classify hyponatremia include these types:
- Hypovolemic hyponatremia: Occurs when the body loses sodium and water; however, the loss of water is greater, which leads to a decrease in sodium concentration and blood volume. This can result from excessive sweating, diarrhea, vomiting, or diuretics.
- Euvolmeic hyponatremia: Occurs from an excess of water in the body with a normal sodium concentration. This can result from conditions including the syndrome of inappropriate antidiuretic hormone secretion (SIADH) and hypothyroidism.
- Hypervolemic hyponatremia: Occurs due to an excess of both sodium and water in the body; however, the water retention is greater, which leads to a dilution of sodium concentration. This can result from conditions including liver cirrhosis, kidney disease, and heart failure.
What causes hyponatremia?
A low sodium level in the blood may result from excess water or fluid in the body, diluting the normal amount of sodium so that the concentration appears low. This type of hyponatremia can be the result of chronic conditions such as kidney failure (when excess fluid cannot be efficiently excreted) and congestive heart failure, in which excess fluid accumulates in the body. SIADH (syndrome of inappropriate anti-diuretic hormone) is a disease whereby the body produces too much anti-diuretic hormone (ADH), resulting in the retention of water in the body. Consuming excess water, for example during strenuous exercise, without adequate replacement of sodium, can also result in hyponatremia.
Hyponatremia can also result when sodium is lost from the body or when both sodium and fluid are lost from the body, for example, during prolonged sweating and severe vomiting or diarrhea.
Medical conditions that can sometimes be associated with hyponatremia are adrenal insufficiency, hypothyroidism, and cirrhosis of the liver.
Finally, several medications can lower blood sodium levels. Examples of these include diuretics, vasopressin, and sulfonylurea drugs.
What are the warning signs of hyponatremia?
When sodium levels in the body are low, water tends to enter cells, causing them to swell. When this occurs in the brain, it is referred to as cerebral edema. Cerebral edema is particularly dangerous because the brain is confined in the skull without room for expansion, and the swelling can lead to brain damage as the pressure increases within the skull. Cerebral edema occurs only in severe cases of hyponatremia.
In chronic hyponatremia, in which the blood sodium levels drop gradually over time, symptoms are typically less severe than with acute hyponatremia (a sudden drop in blood sodium level).
Symptoms can be very nonspecific and can include:
- headache,
- confusion or altered mental state,
- seizures, and
- decreased consciousness, which can proceed to coma and death.
Other possible symptoms include:
- restlessness,
- muscle spasms or cramps,
- weakness, and
- tiredness.
Nausea and vomiting may accompany any of the symptoms.
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Diagnosis of hyponatremia
The symptoms of hyponatremia are nonspecific, so a blood test measuring the sodium level is required to confirm the diagnosis of hyponatremia. Sometimes the medical history (such as prolonged vomiting or excessive sweating) will suggest the diagnosis. In other cases, further blood tests, urine tests, and imaging studies may be needed to determine the exact cause of the hyponatremia.
What is severe hyponatremia?
What happens if your sodium level is 120?
A sodium level of 120 mmol/L (millimoles per liter) is known as a severe case of hyponatremia. This sodium level can significantly affect your body's normal functioning, leading to potentially life-threatening symptoms. These symptoms may include:
- Severe headaches
- Muscle weakness and cramps
- Seizures
- Nausea and vomiting
- Coma
- Confusion, lethargy, and disorientation
If you experience any of the symptoms above, it is important that you seek medical attention immediately.
What is the treatment for hyponatremia?
Mild chronic hyponatremia may not require treatment other than adjustments in diet, lifestyle, slight decrease in water intake, or review and adjustment of medications. For severe or acute hyponatremia, treatment typically involves the intravenous administration of fluids and electrolytes. In these situations, medications are often needed that treat the underlying cause of the hyponatremia as well as medications to manage the accompanying symptoms.
Treatment of hyponatremia depends on the underlying cause and severity of the condition; however, here are some common ways to fix hyponatremia:
- Fluid restriction
- Sodium replacement
- Medications
- Intravenous fluids
- Treating underlying conditions
Medically Reviewed on 3/7/2024
References
Jameson, JL, et al. Harrison's Principles of Internal Medicine, 20th ed. (Vol.1 & Vol.2). McGraw-Hill Education.
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