Doctors order basic blood chemistry tests to assess a wide range of conditions and the function of organs.

Often, blood tests check electrolytes, the minerals that help keep the body's fluid levels in balance, and are necessary to help the muscles, heart, and other organs work properly. To assess kidney function and blood sugar, blood tests measure other substances.

Tests for Electrolytes

Typically, tests for electrolytes measure levels of sodium, potassium, chloride, and bicarbonate in the body.

Sodium plays a major role in regulating the amount of water in the body. Also, the passage of sodium in and out of cells is necessary for many body functions, like transmitting electrical signals in the brain and in the muscles. The sodium levels are measured to detect whether there's the right balance of sodium and liquid in the blood to carry out those functions.

If a child becomes dehydrated because of vomiting, diarrhea, or inadequate fluid intake, the sodium levels can be abnormally high or low, which can cause a child to feel confused, weak, and lethargic, and even to have seizures.

Potassium is essential to regulate how the heart beats. Potassium levels that are too high or too low can increase the risk of an abnormal heartbeat (also called arrhythmias). Low potassium levels are also associated with muscle weakness and cramps.

Chloride, like sodium, helps maintain a balance of fluids in the body. If there's a large loss of chloride, the blood may become more acidic and prevent certain chemical reactions from occurring in the body that are necessary it to keep working properly.

Bicarbonate prevents the body's tissues from getting too much or too little acid. The kidney and lungs balance the levels of bicarbonate in the body. So if bicarbonate levels are too high or low, it might indicate a problem with those organs.

Other Substances Measured

Other blood substances measured in the basic blood chemistry test include blood urea nitrogen and creatinine, which tell how well the kidneys are functioning, and glucose, which indicates whether there is a normal amount of sugar in the blood.

Blood urea nitrogen (BUN) is a measure of how well the kidneys are working. Urea is a nitrogen-containing waste product that's created when the body breaks down protein. If the kidneys are not working properly, the levels of BUN will build up in the blood. Dehydration, excessive bleeding, and severe infection leading to shock can also elevate the BUN levels in the blood.

Creatinine levels in the blood that are too high can indicate that the kidneys aren't working properly. The kidneys filter and excrete creatinine; if they're not functioning properly, creatinine can build up in the bloodstream. Both dehydration and muscle damage also can raise creatinine levels.

Glucose is the main type of sugar in the blood. It comes from the foods we eat and is the major source of energy needed to fuel the body's functions. Glucose levels that are too high or too low can cause problems. The most common cause of high blood glucose levels is diabetes. Other medical conditions and some medications can also cause high blood glucose.

Reviewed by: Yamini Durani, MD
Date reviewed: February 2012