Doctors order basic blood chemistry tests to assess many conditions and learn how the body’s organs are working. Often, blood tests check electrolytes, the minerals that help keep the body's fluid levels in balance and which are necessary to help the muscles, heart, and other organs work properly. Blood chemistry tests also measure other substances that help show how well the kidneys are working and how well the body is absorbing sugars. 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 (from vomiting, diarrhea, or other causes), the sodium levels can be too high or low, which can cause confusion, weakness, lethargy, and even seizures. Potassium is essential to regulating 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. Certain medical problems like dehydration, heart disease, kidney disease, or other illnesses can disrupt the balance of chloride. Testing chloride in these situations helps the doctor tell whether an acid-base imbalance is happening in the body. 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 also can raise BUN levels. 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 working as they should, 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 medicines also can cause high blood glucose. Back to Articles Related Articles Definition: Blood Glucose Level The blood glucose level is the amount of glucose in the blood. Read More Definition: Glucose Glucose is the main type of sugar in the blood and is the major source of energy for the body's cells. Read More Getting a Blood Test (Video) A blood test might sound scary, but it usually takes less than a minute. Watch what happens in this video for kids. Read More Blood Test (Video) These videos show what's involved in getting a blood test and what it's like to be the person taking the blood sample. Read More Blood Test: Phosphorus A phosphorus test looks at levels of phosphorus in a person's blood. Find out why doctors do this test and what's involved for teens. Read More Blood Test: Complete Blood Count This common blood test helps doctors gather information about a person's blood cells and how they're working. Find out why doctors do this test and what's involved for teens. Read More Blood Test: Glucose The blood glucose test, which measures the amount of sugar in the blood, may be done as part of a routine physical or to help diagnose diabetes. Read More Kidneys and Urinary Tract The bean-shaped kidneys, each about the size of a child's fist, are essential to our health. Their most important role is to filter blood and produce urine. Read More Blood Test: Basic Metabolic Panel (BMP) A basic metabolic panel (BMP), commonly ordered as part of routine medical exam, is a set of blood tests that gives information about sugar (glucose) and calcium levels, kidney function, and electrolyte and fluid balance. Read More Blood Test: Comprehensive Metabolic Panel (CMP) A comprehensive metabolic panel (CMP) blood test helps evaluate kidney and liver function, sugar (glucose) and protein levels in the blood, and electrolyte and fluid balance. Read More Urine Test: Creatinine Low levels of creatinine in the urine may point to a kidney disease, certain muscular and neuromuscular disorders, or an obstruction of the urinary tract. Read More Urine Test: Microalbumin-to-Creatinine Ratio The microalbumin-to-creatinine ratio test is most commonly used to screen for kidney problems in teens with diabetes. It may also be used to monitor kidney function in kids and teens who have a kidney disease. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.