Blood Test: Comprehensive Metabolic Panel

What Is a Comprehensive Metabolic Panel and Why Is It Done?

A comprehensive metabolic panel (CMP) is a blood test that provides information about a person's liver and kidneys, body sugar and protein levels, and electrolyte and fluid balance.

Doctors order a CMP test to help diagnose liver or kidney disease, as well as conditions like diabetes. Doctors also use this test to monitor people who have health problems or are taking certain medicines.

Several different tests are done in a comprehensive metabolic panel. It includes all the tests in the basic metabolic panel, in addition to a few others. The good news is you should only need to get blood taken once. The lab uses the same blood sample to run all the tests.

The CMP helps doctors look at:

  • Glucose. The body uses this type of sugar for energy. Abnormal glucose levels can indicate diabetes or hypoglycemia (low blood sugar).
  • Calcium. This mineral plays an important role in muscle contraction, transmitting messages through the nerves, and the release of hormones. High or low calcium levels may be a sign of a hormone imbalance or problems with the kidneys, bones, or pancreas.
  • Albumin and total blood protein. Liver function tests include measuring albumin (the major blood protein produced by the liver), as well as the total amount of all proteins in the blood. When there's a problem with the liver, there can be changes in the amounts of albumin and other proteins it produces.
  • Sodium, potassium, carbon dioxide, and chloride. These electrolytes help balance the body's fluid levels, among other things. They also play a role in regulating heart rhythm, muscle contraction, and brain function. Abnormal levels of these electrolytes may be a sign of heart disease, kidney disease, or dehydration.
  • Blood urea nitrogen (BUN) and creatinine. These waste products are filtered out of the blood by the kidneys. High levels in the blood may be a sign that the kidneys aren't working as well as they should.
  • Alkaline phosphatase (ALP), alanine amino transferase (ALT), aspartate amino transferase (AST), and bilirubin. ALP, ALT, and AST are enzymes found in the liver and other body tissues; bilirubin is produced by the liver. If the blood test shows high levels of these, it may be a sign that the liver isn't working properly.

Preparation

In an emergency, technicians can co the comprehensive metabolic panel test without any special preparation. But the results are more accurate when a person has been fasting. So your doctor may ask you not to eat or drink for 8 to 12 hours before having your blood taken.

You should tell your doctor about any medicines you're taking because certain drugs might alter the test results.

The Procedure

A health professional will usually draw the blood from a vein in your arm — most often on the inside of the elbow, but sometimes on the back of the hand. The technician cleans the skin surface with antiseptic and ties an elastic band (tourniquet) around the upper arm so the veins swell with blood and are easy to see.

Next, it's time for the needle. It should feel like a quick pinprick. Occasionally, it can be hard to find a vein so a nurse, doctor, or technician may need to try more than once. That's not the norm, though — most people's veins are easy to find.

It's best to try to relax and stay still during the procedure since tensing muscles can make it harder and more painful to draw blood. And if you don't want to watch the needle being inserted or see the blood collecting, you don't have to. Look the other way and maybe relax by focusing on saying the alphabet backwards, doing some breathing exercises, thinking of a place that makes you happy, or listening to your favorite music.

The technician will draw the blood so it collects in a vial or syringe. Collecting blood will only take a few minutes. Once the technician has enough blood, he or she removes the needle and covers the area with cotton or a bandage to stop the bleeding. After the test, you may notice some bruising — that's normal and it should go away in a few days. Don't be afraid to ask the technician if you have any questions about the blood draw.

Safety

A blood test is a safe procedure and there are no real risks. Some people may feel faint or lightheaded during a blood test. And, while nobody really loves needles, a few teens have a strong fear of them. If that's you, talk to your doctor since there are ways to make the procedure easier for you.

Results

The blood sample will be processed by a machine. It usually only takes a few hours or a day or so for your doctor to get the results (in an emergency, results on some blood tests can come back much faster). If your doctor thinks the test results show signs of any problems, he or she may decide to do other tests to find out what the problem is and how to treat it.

Reviewed by: Steven Dowshen, MD
Date reviewed: February 2011

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Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.

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