The term "liver function tests" is misleading as most of these tests detect inflammation or liver damage, they do not actually explore the metabolic or secretory functions of liver bile (Liver: Functions of the liver). Such inflammation or lesions may be present even before the liver functions are affected. Liver function tests are blood tests that are a non-invasive way to look for the presence of liver disease (e.g., hepatitis in a blood donation) and to measure the severity and progression of an illness of the liver and its response to treatment.
Laboratory analyses are generally effective for:
- Detect inflammation, lesions or liver dysfunction
- Assess the severity of a liver injury
- Monitor the evolution of the liver disease and the response to a person's treatment
Specify the diagnosis
Hepatic tests are performed on blood samples and measure the levels of enzymes and other substances synthesized by the liver. These substances include:
- Alanine aminotransaminase (ALT)
- Alkaline phosphatase
- Aspartate transaminase (AST)
- Gamma-glutamyl-transpeptidase (gamma-GT)
- Lactate dehydrogenase
The level of some of these substances makes it possible to evaluate whether the liver performs its normal functions of protein production and bile secretion. The level of other substances can detect the presence and degree of inflammation of the liver. What is a normal value for many of these tests can be found in Blood tests? However, the values can sometimes be much higher than normal, usually because a person has another disease.
Why do a liver test?
The LFT test allows, on the one hand, research a possible abnormal liver function, on the other hand, to specify the nature of the anomaly highlighted to understand the origin of the attack better. Among different types of liver dysfunction, we distinguish different syndromes, the main ones of which are hepatic insufficiency (or hepatocellular insufficiency), cytolysis, cholestasis (with or without jaundice) and inflammation. Once the diagnosis is made, the repetition dosages can then monitor the evolution of the anomaly.
What are the examinations required for a liver assessment?
- Liver function tests include the determination of several enzymes, relatively specific to the liver and manufactured (at least partially) by the liver: transaminase (SGPT or ALT and SGOT or AST) the alkaline phosphatase (ALP) the gamma-GlutamylTranspeptidase (gamma -GT) bilirubin
- Other assays are less specific reflections of liver activity but are also markers of hepatic metabolism.
- The determination of blood cholesterol (cholesterolemia): the liver essentially makes cholesterol. Its rate may be increased in case of cholestasis, decreased in the case of hepatocellular insufficiency.
- The albumin dosage: it is a protein made by the liver. Its concentration in the blood is an indirect reflection (and not specific) of the good functioning of the liver. A decrease in its rate rather evokes a hepatocellular insufficiency.
- Fibrinogen: it is a protein made by the liver. A decrease in the level of blood fibrinogen can be observed sometimes in case of hepatic insufficiency.
- The electrophoresis of the proteins: it is a technique which makes it possible to observe a decrease or a relative or absolute increase of each class of proteins. In particular, it evaluates the proper functioning of the liver.
- The prothrombin (PT) level: The prothrombin rate (or the prothrombin time) is a measure of the blood's coagulation rate. It indirectly helps to evaluate the state of the liver, since coagulation proteins are made in the liver. Prolongation of TP may indicate hepatocellular failure.