Serum Electrolytes

Your Care Explained > Tests and Procedures : Serum Electrolytes

Electrolytes are electrically charged minerals that help move nutrients into and wastes out of the body’s cells, maintain a healthy water balance and help stabilize the body’s acid level.

A blood test that measures the main electrolytes in the body—sodium, potassium, chloride and bicarbonate (CO2)—can be used to evaluate symptoms of heart disease and monitor the effectiveness of treatments for high blood pressure, heart failure and liver and kidney disease.

Understanding Electrolytes

The balance of sodium, potassium, chloride and bicarbonate in the blood is a good indicator of how well the kidneys and heart are functioning. Knowing which electrolytes are out of balance can help your doctor determine a course of treatment.


Sodium is regulated by the kidneys and adrenal glands. Low sodium levels are caused by kidney disease and adrenal disease, diuretics, diarrhea, and occasionally conditions that cause fluid buildup in the body; the most common cause of high sodium is dehydration. Normal sodium levels are 136 to 142 mmol/L.


Potassium concentrations that are too high can be due to kidney disease or drugs that can decrease potassium excretion from the body. Low potassium can be a consequence of using certain diuretics or of dehydration. Normal potassium levels are 3.5 to 5.0 mmol/L.


Chloride levels usually fluctuate with sodium levels. Low chloride levels can occur with chronic lung disease, prolonged vomiting, and with loss of acid from the body, called metabolic alkalosis. High chloride levels may result from dehydration, but can also occur with other problems that cause high blood sodium, such as kidney disease. The normal range of chloride levels is 98 to 108 mmol/L.


The total CO2 test measures the total amount of carbon dioxide in the blood, mostly in the form of bicarbonate, which is excreted and reabsorbed by the kidneys. CO2 helps maintain the body’s acid-base balance (pH) in concert with sodium, potassium and chloride. Bicarbonate levels that are higher or lower than normal may signify an acid/base or electrolyte imbalance, often due to dehydration or drinking too much water. The normal range of CO2 is 23 to 32 mmol/L.

Date Last Modified: January 21, 2011

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