What Is a Blood Test?
A blood test is when a sample of blood is taken from the body to be tested in a
lab. Doctors order blood tests to check things such as the levels of glucose, hemoglobin,
or white blood cells. This can help them detect problems like a disease or medical
condition. Sometimes, blood tests can help them see how well an organ (such as the
liver or kidneys) is working.
What Is a Comprehensive Metabolic Panel (CMP)?
The comprehensive metabolic panel (CMP) is a blood test that gives doctors information
about the body's fluid balance, levels of electrolytes like sodium and potassium,
and how well the kidneys and
liver are working.
Why Are Comprehensive Metabolic Panels Done?
A CMP is done to learn information about the levels of:
- Glucose,
a type of sugar used by the body for energy. High glucose levels may point to diabetes.
- Electrolytes:
- Calcium,
which plays an important role in how muscles and nerves work.
- Sodium, potassium, carbon dioxide, and chloride,
which help control the body's fluid levels and its acid-base balance. Normal levels
of these electrolytes help keep cells in the body working as they should.
- Blood urea nitrogen (BUN) and creatinine, which
are waste products filtered out of the blood by the kidneys. These levels show how
well the kidneys are working.
- Albumin and total protein, which are needed
to build and maintain muscles, bones, blood, and organ tissue. Low levels may be seen
with liver or kidney disease, or nutritional problems.
- Liver tests: Alkaline phosphatase (ALP), alanine
aminotransferase (ALT), aspartate
aminotransferase (AST), and bilirubin.
When these levels are high, it can be a sign of a problem with the liver.
How Should We Prepare for a CMP?
Your child may be asked to stop eating and drinking for 8 to 12 hours before a
CMP. Tell your doctor about any medicines your child takes because some drugs might
affect the test results.
Wearing a T-shirt or short-sleeved shirt for the test can make things easier for
your child, and you also can bring along a toy or book as a distraction.
How Is a CMP Done?
Most blood tests take a small amount of blood from a vein. To do that, a health
professional will:
- clean the skin
- put an elastic band (tourniquet) above the area to get the veins to swell with
blood
- insert a needle into a vein (usually in the arm inside of the elbow or on the
back of the hand)
- pull the blood sample into a vial or syringe
- take off the elastic band and remove the needle from the vein
In babies, blood draws are sometimes done as a "heel stick collection." After cleaning
the area, the health professional will prick your baby's heel with a tiny needle (or
lancet) to collect a small sample of blood.
Collecting a sample of blood is only temporarily uncomfortable and can feel like
a quick pinprick.
Can I Stay With My Child During a CMP?
Parents usually can stay with their child during a blood test. Encourage your child
to relax and stay still because tensing muscles can make it harder to draw blood.
Your child might want to look away when the needle is inserted and the blood is collected.
Encourage your child to relax by taking slow deep breaths or singing a favorite song.
How Long Does a CMP Take?
Most blood tests take just a few minutes. Occasionally, it can be hard to find
a vein so the health professional may need to try more than once.
What Happens After a CMP?
The health professional will remove the elastic band and the needle and cover the
area with cotton or a bandage to stop the bleeding. Afterward, there may be some mild
bruising, which should go away in a few days.
When Are CMP Results Ready?
Blood samples are processed by a machine, and it may take a few hours to a day
for the results to be available. If the test results show signs of a problem, the
doctor might order other tests to figure out what the problem is and how to treat
it.
Are There Any Risks From CMPs?
A comprehensive metabolic panel is a safe procedure with minimal risks. Some kids
might feel faint or lightheaded from the test. A few kids and teens have a strong
fear of needles. If your child is anxious, talk with the doctor before the test about
ways to make the procedure easier.
A small bruise or mild soreness around the blood test site is common and can last
for a few days. Get medical care for your child if the discomfort gets worse or lasts
longer.
If you have questions about the CMP, speak with your doctor or the health professional
doing the blood draw.
