Blood Test: Comprehensive Metabolic Panel (CMP)
What It Is
A comprehensive metabolic panel (CMP) is a blood test that provides information about:
- how the kidney and liver are functioning
- sugar (glucose) and protein levels in the blood
- the body's electrolyte and fluid balance
Why It's Done
A CMP may be ordered as part of routine medical exam or physical, or to help diagnose conditions such as diabetes, or liver or kidney disease. The CMP may also be used to monitor chronic conditions, or when a patient is taking medications that can cause certain side effects.
The CMP helps evaluate:
- Glucose, a type of sugar used by the body for energy. Abnormal levels can indicate diabetes or hypoglycemia (low blood sugar).
- Calcium, which plays an important role in muscle contraction, transmitting messages through the nerves, and the release of hormones. Elevated or decreased calcium levels may indicate a hormone imbalance or problems with the kidneys, bones, or pancreas.
- Albumin and total blood protein, which are needed to build and maintain muscles, bones, blood, and organ tissue. The CMP measures albumin specifically (the major blood protein produced by the liver), as well as the amount of all proteins in the blood. Low levels may indicate liver or kidney disease or nutritional problems.
- Sodium, potassium, carbon dioxide, and chloride (electrolytes), which help regulate the body's fluid levels and its acid-base balance. They also play a role in regulating heart rhythm, muscle contraction, and brain function. Abnormal levels also may occur with heart disease, kidney disease, or dehydration.
- Blood urea nitrogen (BUN) and creatinine, which are waste products filtered out of the blood by the kidneys. Increased concentrations in the blood may signal a decrease in kidney function.
- Alkaline phosphatase (ALP), alanine amino transferase (ALT), aspartate amino transferase (AST), and bilirubin; ALP, ALT, and AST are liver enzymes; bilirubin is produced by the liver. Elevated concentrations may indicate liver dysfunction.
It may help to have your child wear a short-sleeved shirt to allow easier access for the technician to draw the blood. Usually no special preparation is needed, but sometimes your doctor may ask for the test to be performed after fasting. That means your child may be asked not to eat for 8 to 12 hours before the test.
A health professional will usually draw the blood from a vein. For an infant, the blood may be obtained by puncturing the heel with a small needle (lancet). If the blood is being drawn from a vein, the skin surface is cleaned with antiseptic, and an elastic band (tourniquet) is placed around the upper arm to apply pressure and cause the veins to swell with blood. A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.
After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting blood for this test will only take a few minutes.
What to Expect
Either method (heel or vein withdrawal) of collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a few days.
Getting the Results
The blood sample will be processed by a machine. Parts of a CMP may be available in minutes in an emergency, but more commonly the full test results come after a few hours or the next day.
If any of the CMP results are abnormal, further testing may be necessary to determine what's causing the problem and how to treat it.
The CMP test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn, such as:
- fainting or feeling lightheaded
- hematoma (blood accumulating under the skin causing a lump or bruise)
- pain associated with multiple punctures to locate a vein
Helping Your Child
Having a blood test is relatively painless. Still, many kids are afraid of needles. Explaining the test in terms your child can understand might help ease some of the fear.
Allow your child to ask the technician any questions he or she might have. Tell your child to try to relax and stay still during the procedure, as tensing muscles and moving can make it harder and more painful to draw blood. It also may help if your child looks away when the needle is being inserted into the skin.
If You Have Questions
If you have questions about the CMP test, speak with your doctor. You also can talk to the technician before the procedure.