Blood tests usually can be done in a doctor's office or in a lab where technicians are trained to take blood. When only a small amount of blood is needed, the sample can sometimes be taken from a baby by sticking a heel and from an older child by sticking a finger with a small needle.
If a larger blood sample is needed, the technician drawing the blood will clean the skin, insert a needle into a vein (usually in the arm or hand) and withdraw blood. In kids, it sometimes takes more than one try. A bandage and a cotton swab will help stop the flow of blood when the needle is removed.
Blood tests can be scary for kids, so try to be a calming presence during the procedure. Holding your child's hand or offering a stuffed animal or other comforting object can help. Tell your child that it may pinch a little, but that it will be over soon. With younger kids, try singing a song, saying the alphabet or counting together while the blood is being drawn.
Common blood tests include:
- Complete blood count (CBC). A CBC measures the levels of different types of blood cells. By determining if there are too many or not enough of each blood cell type, a CBC can help to detect a wide variety of illnesses or signs of infection.
- Blood chemistry test. Basic blood chemistry tests measure the levels of certain electrolytes, such as sodium and potassium, in the blood. Doctors typically order them to look for any sign of kidney dysfunction, diabetes, metabolic disorders, and tissue damage.
- Blood culture. A blood culture may be ordered when a child has symptoms of an infection – such as a high fever or chills – and the doctor suspects bacteria may have spread into the blood. A blood culture shows what type of germ is causing an infection, which will determine how it should be treated.
- Lead test. The American Academy of Pediatrics (AAP) recommends that all toddlers get tested for lead in the blood at 1 and 2 years of age since young kids are at risk for lead poisoning if they eat or inhale particles of lead-based paint. High lead levels can cause stomach problems and headaches and also have been linked to some developmental problems.
- Liver function test. Liver function tests check to see how the liver is working and look for any sort of liver damage or inflammation. Doctors typically order one when looking for signs of a viral infection (like mononucleosis or viral hepatitis) or liver damage from other health problems.