The hepatic function panel, also known as liver function tests, is a group of seven tests used to evaluate the liver for injury, infection, or inflammation.
The liver plays important roles: It stores energy from food, makes proteins, and helps remove toxins. The liver also makes bile, a fluid that helps in digestion.
Why It's Done
Liver function tests help doctors find out whether the liver has been damaged. If your child is experiencing symptoms of liver disease — including jaundice (yellowish skin or eyes), dark urine, nausea, vomiting, or abdominal swelling — these tests may be ordered. They may also be done to help diagnose viral infections (such as hepatitis or mononucleosis) or to monitor medications that can cause liver-related side effects.
The hepatic function panel evaluates:
Alanine aminotransferase (ALT). This enzyme, found in the liver, plays a role in metabolism, the process that converts food into energy. If the liver is injured, ALT is released into the bloodstream. Its levels are especially high with acute hepatitis.
Alkaline phosphatase (ALP). This enzyme is found in the liver, bones, intestines, kidneys, and other organs. Kids and teens normally have higher levels of ALP than adults, even when they're healthy, due to bone growth. But ALP levels can also increase when kids have viral infections, liver diseases, or blocked bile ducts.
Aspartate aminotransferase (AST). This enzyme, which plays a role in processing proteins, is found in the liver, heart, muscles, and kidneys. When the liver is injured or inflamed, levels of AST in the blood usually rise.
Total bilirubin and direct bilirubin. Bilirubin is a byproduct of the normal breakdown of red blood cells. It usually passes through the liver and is excreted from the body. But if that doesn't happen due to a liver disease, bilirubin levels in the blood can rise and the skin can take on the yellow discoloration known as jaundice. Tests for bilirubin may be total (measuring the level of all of the bilirubin in the blood) or direct (measuring only bilirubin that has been processed by the liver and attached to other chemicals).
Albumin and total protein. Protein is needed to build and maintain muscles, bones, blood, and organ tissue. Sometimes when there's a problem with the liver, it can't make proteins as well, so protein levels decrease. Liver function tests measure albumin specifically (the major blood protein produced by the liver), as well as the total amount of all proteins in the blood.
Although the hepatic function panel can be done without any preparation, it's more accurate when performed after fasting. Your child may be asked to stop eating and drinking for 10 to 12 hours before this blood test. You should also tell your doctor about any medications your child is taking because certain drugs might alter the test results.
On the day of the test, having your child wear a short-sleeve shirt can make things easier for the technician who will be drawing the blood.
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.
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 day or so.
Getting the Results
The blood sample will be processed by a machine. Parts of a hepatic function panel 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 results seem to point to liver damage or disease, further testing may be necessary to determine what's causing the problem and how to treat it.
The hepatic function panel is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn:
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 children 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 hepatic function panel, speak with your doctor. You can also talk to the technician before the procedure.