Hyponatremia
(Low Blood Sodium)

Medical Author:
Medical Editor:

Hyponatremia facts

  • Hyponatremia refers to a low level of sodium in the blood.
  • Hyponatremia may result from excess fluid in the body relative to a normal amount of sodium, or it may be due to a loss of sodium and body fluid.
  • Symptoms are nonspecific and can include mental changes, headache, nausea and vomiting, tiredness, muscle spasms, and seizures.
  • Severe hyponatremia can lead to coma and can be fatal.
  • Treatment of hyponatremia involves intravenous fluid and electrolyte replacement, medications to manage the symptoms of hyponatremia, as well as any treatments for the underlying cause.

What is hyponatremia (low blood sodium)?

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). Results may vary slightly among different laboratories.

What causes hyponatremia (low blood sodium)?

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 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, a number of medications can lower blood sodium levels. Examples of these include diuretics, vasopressin, and the sulfonylurea drugs.

Medically Reviewed by a Doctor on 12/4/2013

Patient Comments

Viewers share their comments

Hyponatremia - Experience Question: Please describe your experience with Hyponatremia.
Hyponatremia (Low Blood Sodium) - Symptoms Question: What are the symptoms associated with your hyponatremia?
Hyponatremia (Low Blood Sodium) - Diagnosis Question: What tests or exams led to a diagnosis of low blood sodium?
Hyponatremia (Low Blood Sodium) - Treatment Question: What kinds of treatment have you received for your low blood sodium?
Drinking not enough fluids and replacing electrolytes such as sodium can lead to hyponatremia (low blood sodium levels), which can be life-threatening.

Dehydration & Exercise = Hyponatremia (Low Blood Sodium)

Viewer Question: My trainer is always telling me to stay hydrated. How much water should I drink when exercising? What will happen if I drink too much?

Fitness Expert's Response: The National Athletic Trainers' Association recommends the following hydration guidelines for exercise:

  1. Two to three hours pre-exercise: 17 to 20 fluid ounces of water or sports drink.
  2. Ten to 20 minutes pre-exercise: 7 to 10 ounces of water or sports drink.
  3. During exercise: Fluid replacement should approximate sweat and urine losses and at least maintain hydration at less than 2% body weight reduction. This generally requires 7 to 10 ounces of water or sports drink every 10 to 20 minutes.

STAY INFORMED

Get the Latest health and medical information delivered direct to your inbox!