LFTs are group of clinical biochemistry laboratory blood assays designed to give information about the state of a patient’s liver. As the liver performs it’s various functions it makes a number of chemicals that pass into the bloodstream and bile. Various liver disorders alter the blood level of these chemicals. Some of these chemicals can be measured in a blood sample. Some tests that are commonly done on a blood sample are called ‘LFTs’ (liver function tests).
Liver function tests can be classified as:
a. Tests of excretion by the liver.
b. Evaluation of synthesis in liver.
c. Evaluation of enzyme activity.
Liver function tests are most often employed to determine:
i. The presence of liver disease.
ii. The type of liver disease.
iii. The extent and progression of liver disease.
Note: The diagnosis of liver disease depends upon a complete history, complete physical examination, and evaluation of liver function tests and further invasive and noninvasive tests
• Alanine Aminotransferase (ALT) =SGPT:
ALT is the enzyme produced within the cells of the liver. The level of ALT abnormality is incre ased in conditions where cells of the liver have been inflamed or undergone cell death. As the cells are damaged, the ALT leaks into the bloodstream leading to a rise in the serum levels. Any form of hepatic cell damage can result in an elevation in the ALT. ALT is the most sensitive marker for liver cell damage.
• Clinical applications of ALT assays are confined mainly to evaluation of hepatic disorders.
• Higher elevations are found in hepatocellular disorders than in extrahepatic or intrahepatic obstructive disorders.
• In acute inflammatory conditions of the liver, ALT elevated higher than AST. (More specific than AST).
• Aspartate Aminotransferase (AST) =SGOTU:
This enzyme also reflects damage to the hepatic cell. It is less specific for liver disease. It may be elevated and other conditions such as a myocardial infarct (heart attack). Although AST is not a specific for liver as the ALT, ratios between ALT and AST are useful to physicians in assessing the etiology of liver enzyme abnormalities.
• Alkaline Phosphatase (ALP):
Alkaline phosphatase is an enzyme, which is associated with the biliary tract. It is not specific to the biliary tract. It is also found in bone and the placenta. If the alkaline phosphatase is elevated, biliary tract damage and inflammation should be considered.
One of the more common methods to assess the etiology of the elevated alkaline phosphatase is to determine whether the GGT is elevated or whether other function tests are abnormal (such as bilirubin). Alkaline phosphatase may be elevated in primary biliary cirrhosis, alcoholic hepatitis
• Gamma Glutamic Transpeptidase (GGT):
This enzyme is also produced by the bile ducts. However, it is not very specific to the liver or bile ducts. It is used often times to confirm that the alkaline phosphatase is of the hepatic etiology. Medications commonly cause GGT to be elevated. Liver toxins such as alcohol can cause increases in the GGT.
– Collect blood and prepare serum in an appropriate tube.
– Measure ALT and AST levels.
– Compare the results to the normal values.
Assay for Enzyme Activity:
• Alanine + α-Ketoglutarate [ALT] =Glutamate + Pyruvate
• Pyruvate + NADH + H [LDH] =Lactate + NAD
• The rate of decrease in concentration of NADH, measured photometrically, is proportional to the catalytic concentration of ALT present in the sample. Reference Range: Normal: 6 – 37 U/L.
• Many drugs may cause falsely increased and decreased ALT levels.
• Therapeutic heparin increases ALT.
• Hemolysed blood increases ALT.