Normal Serum Sodium Levels

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Sodium ions play a critical role in the human body. They are involved in fluid balance, nerve functioning, heart activity and other metabolic activities. Generally, doctors will order serum sodium as part of a routine laboratory work-up, to monitor various medical conditions, or when they suspect a fluid imbalance.

The Test

Serum sodium levels are measured through a standard venous blood draw. Patients are advised to discontinue medications that will interfere with serum sodium levels. Drugs that can increase levels include birth control pills, non-steroidal anti-inflammatory drugs and corticosteroids. Those that can decrease serum levels include diuretics, morphine, carbamazepine and sulfonylureas.

The Results

A normal serum sodium level is between 135 and 145 milliequivalents per liter. As this value can vary from laboratory to laboratory, it is important to consult with your physician to get a proper assessment. Results that show a normal serum sodium level can indicate adequate fluid-balance, proper management of various medical conditions or adequate metabolic functioning. Abnormal results, however, can indicate a number of different medical conditions. To help determine the cause, your doctor will evaluate the total amount of fluid in your body by examining your skin, as well as your ankles, feet and legs.

Elevated Serum Levels

Serum sodium levels above 145 milliequivalents per liter are considered elevated. The condition is termed hypernatremia. Your doctor will likely try to determine what might be causing this by evaluating the total amount of fluid in your body. If the fluid in your body is shown to be low, you may have fluid loss from such things as diarrhea, excessive sweating or the use of diuretics. If your total body water is determined to be normal, the high sodium levels may be from diabetes insipidus; that is, too little of the hormone vasopressin. If your total body fluid is shown to be high, you may have hyperaldosteronism or Cushing syndrome.

Decreased Serum Levels

Serum sodium levels below 135 milliequivalents per liter are considered decreased. Lower than normal levels are called hyponatremia. As in the case of elevated serum levels, your doctor will probably try to determine the cause by evaluating your body's total fluid amount. Low total body water and sodium levels may be a result of dehydration, vomiting or diarrhea, or ketonuria. Normal total body fluid may mean you have hypothryroidism, Addison's disease or too much of the hormone vasopressin. Increased levels of total body water may indicate congestive heart failure, kidney disease or cirrhosis of the liver.


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Understanding serum sodium levels can provide valuable information concerning your health. Nevertheless, it is important to interpret these values within the context of your total clinical picture. It is best to consult with your physician to better understand the significance of your serum sodium levels.