The Test Sample
What is being tested?
A liver panel is a group of tests that are performed together to detect, evaluate, and monitor liver disease or damage. The liver is one of the largest organs in the body and is located in the upper right-hand part of the abdomen and behind the lower ribs. The liver metabolizes and detoxifies drugs and substances that are harmful to the body. It produces blood clotting factors, proteins, and enzymes, helps maintain hormone balances, and stores vitamins and minerals. Bile, a fluid produced by the liver, is transported through ducts directly to the small intestine to help digest fats or to the gallbladder to be stored and concentrated for later use.
A variety of diseases and infections can cause acute or chronic damage to the liver, causing inflammation (hepatitis), scarring (cirrhosis), bile duct obstructions, liver tumors, and liver dysfunction. Alcohol, drugs, some herbal supplements, and toxins can also pose a threat. A significant amount of liver damage may be present before symptoms such as jaundice, dark urine, light-colored stools, itching (pruritus), nausea, fatigue, diarrhea, and unexplained weight loss or gain emerge. Early detection is essential in order to minimize damage and preserve liver function.
The liver panel measures enzymes, proteins, and substances that are produced or excreted by the liver and are affected by liver injury. Some are released by damaged liver cells and some reflect a decrease in the liver's ability to perform one or more of its functions. When performed together, these tests give the doctor a snapshot of the health of the liver, an indication of the potential severity of any liver injury, change in liver status over time, and a starting place for further diagnostic testing.
The panel usually consists of several tests that are run at the same time on a blood sample. These typically include:
- Alanine aminotransferase (ALT) – an enzyme mainly found in the liver; the best test for detecting hepatitis
- Alkaline phosphatase (ALP) – an enzyme related to the bile ducts but also produced by the bones, intestines, and during pregnancy by the placenta (afterbirth); often increased when bile ducts are blocked
- Aspartate aminotransferase (AST) – an enzyme found in the liver and a few other organs, particularly the heart and other muscles in the body
- Bilirubin – two different tests of bilirubin often used together (especially if a person has jaundice): total bilirubin measures all the bilirubin in the blood; direct bilirubin measures a form that is conjugated (combined with another compound) in the liver
- Albumin – measures the main protein made by the liver; the level can be affected by liver and kidney function and by decreased production or increased loss
- Total protein (TP) – measures albumin and all other proteins in blood, including antibodies made to help fight off infections
Depending on the doctor and the laboratory, other tests that may be included in a liver panel are:
- Gamma-glutamyl transferase (GGT) – another enzyme found mainly in liver cells
- Lactate dehydrogenase (LDH) – an enzyme released with cell damage; found in cells throughout the body
- Prothrombin time (PT) – the liver produces proteins involved in the clotting (coagulation) of blood; the PT measures clotting function and, if abnormal, may indicate liver damage.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Some of the tests that may be included in the panel may require fasting overnight with only water permitted. Follow any instructions provided.