Low blood sodium is a condition in which the amount of sodium in the blood is lower than normal. The medical name of this condition is hyponatremia.
Sodium is found mostly in the body fluids outside the cells. Sodium is an electrolyte (mineral). It is very important for maintaining blood pressure. Sodium is also needed for nerves, muscles, and other body tissues to work properly.
When the amount of sodium in fluids outside cells drops below normal, water moves into the cells to balance the levels. This causes the cells to swell with too much water. Brain cells are especially sensitive to swelling, and this causes many of the symptoms of low sodium.
With low blood sodium (hyponatremia), the imbalance of water to sodium is caused by one of three conditions:
Low blood sodium can be caused by:
Common symptoms include:
The health care provider will perform a complete physical examination and ask about your symptoms. Blood and urine tests will be done.
Lab tests that can confirm and help diagnose low sodium include:
The cause of low sodium must be diagnosed and treated. If cancer is the cause of the condition, then radiation, chemotherapy, or surgery to remove the tumor may correct the sodium imbalance.
Other treatments depend on the specific type of hyponatremia.
Treatments may include:
Outcome depends on the condition that is causing the problem. Low sodium that occurs in less than 48 hours (acute hyponatremia), is more dangerous than low sodium that develops slowly over time. When sodium level falls slowly over days or weeks (chronic hyponatremia), the brain cells have time to adjust and swelling may be minimal.
In severe cases, low sodium can lead to:
When your body’s sodium level drops too much, it can be a life-threatening emergency. Call your provider right away if you have symptoms of this condition.
Treating the condition that is causing low sodium can help.
If you play sports or do other vigorous activity, drink fluids such as sports drinks that contain electrolytes to keep your body's sodium level in a healthy range.
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.