Liver function test refers to a group of tests that screen the blood for enzymes and proteins produced in the liver. By determining the level of these substances, this group of tests can determine the presence of liver disease or damage. An abnormal result in any of the tests may indicate the presence of liver disease. The farther the result is from the normal range, the more significant the disease is, according to MayoClinic.com.
Function of the Liver
The liver filters blood in order to regulate the level of all chemicals in the blood and break down nutrients in the blood. At any given time, the liver holds approximately 13 percent of the total blood volume, according to the Lucile Packard Children's Hospital at Stanford.
The liver produces bile to help break down fats and carry out waste products from digested food. The liver also produces albumin, the most abundant protein found in blood. Other functions include the production of necessary enzymes, the storage of iron and the conversion of ammonia to urea.
When to Perform the Test
The presence of certain symptoms may prompt a doctor to suspect liver disease or damage. According to Lab Tests Online, these symptoms include, but are not limited to, fatigue, weakness, nausea, vomiting, abdominal swelling, dark urine, light colored stool and itchy skin. Jaundice, the yellowing of the skin and whites of the eyes, also indicates a malfunction of the liver.
Patients with a history of certain conditions possess an increased risk for developing liver disease. This includes heavy alcohol use, exposure to hepatitis viruses, a family history of liver disease or the use of illegal drugs.
Blood Components Detected
A liver function test determines the level of several types of enzymes in the blood. This includes alanine aminotransferase, or ALT; alkaline phosphatase, or ALP; aspartate aminotransferase, or AST; gamma-glutamyl transferase, or GGT; and lactate dehydrogenase, or LDH. Liver function tests also reveal the level of bilirubin and albumin in the blood and provide the total amount of protein in the blood. Prothrombin, a protein produced by the liver, helps blood to clot. One of the liver function tests indicates the prothrombin time, the amount of time it takes for blood to clot.
Types of Liver Problems
An abnormal reading on any of the components of the liver function test can indicate one of many different liver problems. Cirrhosis of the liver occurs when scar tissue replaces health liver tissue, usually caused by excessive alcohol or drug use. Hepatitis, a viral infection, causes inflammation of the liver that interferes with liver function. The liver can develop tumors that inhibit function. In addition, conditions of the gall bladder, such as the formation of gall stones, can block the bile ducts, therefore blocking substances from leaving the liver.
Abnormal Test Results
High levels of liver enzymes, including ALT and AST, in the bloodstream indicate the presence of liver inflammation or damage. High levels of the enzymes GGT and ALP can indicate a blockage of the bile ducts, according to the AIDS Treatment Data Network. Very low levels of albumin and high levels of bilirubin indicate liver disease. A prothrombin time longer than normal can also indicate liver disease.
