Liver function tests, also known as liver panels, are blood tests that examine levels of proteins and enzymes. They are usually used to determine if a disease is present or to manage the treatment of patients with known liver diseases. The tests look at the proteins albumin and bilirubin as well as enzymes, including alanine transaminase, aspartate transaminase and alkaline phosphatase.
Hepatitis
Acute viral hepatitis--inflammation of the liver--can drastically increase liver enzymes. Chronic hepatitis can also cause elevated levels of liver enzymes. It is important to note that a subsection of individuals with chronic hepatitis may have normal liver function tests. The American Academy of Family Physicians explains that this is most likely because the disease kills many of the liver cells, called hepatocytes, that normally produce the enzymes measured in the tests.
Chronic Alcohol Use
Chronic alcohol use leads to several diseases that can cause abnormal liver function tests. Furthermore, continued alcohol use in the presence of disease increases the presence of abnormalities in tests. Cirrhosis and alcoholic hepatitis, for example, increase levels of aspartate aminotransferase and alanine aminotransferase, according to the American Association of Clinical Chemistry. Alcoholic liver disease also elevates the amount of aspartate aminotransferase in relation to alanine aminotransferase, in part because alcoholics lack the necessary vitamins needed for the liver to make the alanine aminotransferase.
Medication
Some medications may affect the results of liver function tests. For example phenytoin, an anti-convulsant drug used to treat seizures, may raise levels of an enzyme called gamma-glutamyltransferase. An overdose of the over-the-counter pain medication acetaminophen can also lead to abnormal test results, especially in chronic alcohol abusers.
Bone and Muscle Conditions
Since alanine transaminase and aspartate transaminase are also found in bone and muscle, abnormal levels do not necessarily indicate presence of liver disease. Elevated amounts of either may result from muscle exertion or injury, including the heart muscle. As noted by the American Academy of Family Physicians, liver function tests used to be part of a doctor's toolkit in diagnosing heart attacks. Bone injuries such as a fracture can affect levels of aspartate transaminase.
Other Causes
Pregnancy may cause abnormal liver function test results. It is normal, however, for certain liver enzymes to increase during the third trimester. In addition, the protein albumin is often lower than normal in pregnant women. Obesity may also affect liver function tests. The high amount of fat in the livers of obese individuals affects the levels of aspartate transaminase and alanine transaminase. According to the American Academy of Family Physicians, weight loss can move levels of alanine transaminase back toward the normal range.
