A liver function test scans the blood for a variety of enzymes and proteins that could indicate liver disease when found at elevated or abnormally low levels. The enzymes and proteins are not exclusive to liver function, however, so the test can indicate problems with other organs as well. The normal ranges are provided by the Mayo Clinic, but normal levels can vary from person to person and can be skewed by diets or medication. The further off a result is from the normal levels, the more likely it is to indicate liver disease.
Alanine Transaminase (ALT)
ALT is an enzyme in liver cells. Normal levels are between 7 and 55 units per litre. High levels might indicate such health problems as viral hepatitis, congestive heart failure or mononucleosis, though exercise also elevates levels.
Aspertate Transaminase (AST)
Like ALT, AST is an enzyme found in liver cells. Normal levels are between 8 and 48 units per litre. AST also is found in skeletal muscles, the heart, brain, and kidneys. Elevated levels could indicate damage to those organs as well as the liver.
Alkaline Phosphatese (ALP)
ALP is an enzyme in the liver biliary ducts, bone and placental tissue. Normal levels are between 45 and 115 units per litre. High levels might indicate bile duct blockage, cirrhosis, hepatitis, or a number of other liver problems. It also can indicate a cancer's spread to the bone. Low levels are rarer, but they can indicate forms of anaemia or leukaemia.
Albumin is a protein manufactured by the liver, and the total protein number measures both it and globulin levels. Normal albumin levels are between 3.5 and 5.0 grams per decilitre, and normal total protein levels are between 6.3 and 7.9 grams per decilitre. Low levels indicate diseases of the liver or kidney, digestive problems or malnutrition. Dehydration can cause elevated levels.
Bilirubin is a byproduct in the blood removed by liver functions. Normal levels are between 0.1 and 1.0 milligrams per decilitre. High levels of bilirubin cause jaundice and might indicate viral hepatitis, cirrhosis, anaemia, or bile duct blockage.
Gamma Glutamyl Transpeptidase (GGT)
GGT is an enzyme found mostly in the liver. Normal levels are between 0 and 30 units per litre. Elevated levels indicate alcohol abuse.