The term liver function test is not accurate, because most of these tests detect inflammation or liver damage and not the liver’s metabolic or biliary functions ( liver functions ). Such inflammation or injury may be present before the actual functioning of the liver is affected. Liver function tests are blood tests that represent a noninvasive way of detecting the presence of liver disease (eg, hepatitis in blood donations) and measure the severity and progression of the liver and its response to treatment.
Laboratory tests are generally effective for the following:
- Detect liver dysfunction
- Assess the severity of liver damage
- Monitor the evolution of a liver disease and the person’s response to treatment
- Specify or diagnose
Liver function tests are performed on blood samples and measure levels of enzymes and other substances produced by the liver. These substances include
- Alanina transaminase (ALT)
- Alkaline phosphatase
- Aspartate transaminase (AST)
- Gama-glutamil transpeptidase
- Lactic dehydrogenase
- Antimitochondrial antibodies
The concentrations of some of these substances measure the efficiency with which the liver performs its normal functions of protein synthesis and bile secretion. Concentrations of other substances detect the presence and degree of hepatic inflammation. What constitutes a normal value for many of these tests can be found in Blood Tests * . However, sometimes the values may be well above normal, usually because the person has another disorder.
A liver function test is the prothrombin time (PT), used to calculate the international normalized ratio (RNI). Both TP and RNI are measurements of the time it takes for blood to coagulate (the liver synthesizes some proteins necessary for blood clotting, called blood coagulation factors). An abnormal PD or RNI may indicate an acute liver disorder. In chronic liver disorders, increased TP or RNI typically indicates progression to liver failure.
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