The liver is the largest gland and largest organ in the body; it is estimated to have over 500 functions within the body. Some of the most important functions include the production of bile to aid digestion, combating infection via mobilisation of the bodies defence mechanisms, the removal of harmful substances (drugs and toxins) not excreted by the kidneys, the manufacture and regulation of many hormones, manufacture of essential proteins and enzymes as well as the production of energy from the breakdown of food etc.
The term Liver disease or hepatic disease is used to describe any disorder of the Liver that affects its ability to function properly. There are over 100 different types of liver disease including hepatitis, cirrhosis, fatty liver disease and cancer. Liver disease can be hereditary, the result of drug/alcohol abuse or can even be caused by viruses in the case of hepatitis A. B and C.
The most common and probably the most recognisable symptom of liver disease is jaundice many other symptoms are vague and similar for many different disease states it is therefore necessary to carry out blood tests to confirm or rule out liver disease. The most common tests include:
Tested to give an indication of the degree of inflammation. They are present in hepatocytes and leak into the bloodstream if liver cells are damaged or injured. Perhaps ALT is the most specific marker as AST can also be elevated in other disease states.
The liver cells absorb Bilirubin removing it from the blood, it is then secreted into the bile. Increased levels of Bilirubin can therefore indicate Liver damage.
Found predominantly in the bile ducts increased levels in the blood can therefore indicate an obstruction of the bile duct preventing bile from being released and transported as necessary.
Increased levels can indicate the use of drugs or alcohol it is often tested in combination with ALP to ensure any increase in ALP is linked with the liver.
An enzyme that converts lactate to Pyruvate, levels in the blood can become increased after alcohol consumption, levels are also increased after the use of certain drugs.
Albumin is the main component of Total Protein and is made specifically by the liver, a decrease in albumin levels can therefore be a good indicator of liver disease.
Bile Acids provides a highly specific marker for use in the diagnosis and monitoring of various liver conditions supplying information that conventional markers like AST and ALT cannot. It is also one of the most sensitive markers for the early detection of liver dysfunction. Abnormal levels of Bile Acids are associated with obstetric cholestasis in pregnant women, hepatitis, liver sclerosis and liver cancer.
Although we are looking for elevated levels of the above parameters, negative results can also be of value as they indicate a low probability of significant disease. The standard liver function test profile measures dysfunction rather than function however can help categorise the patient as hepatocellular, cholestatic, chronic hepatitis or cirrhotic. Liver function tests such as those listed above can be used to answer 3 questions; is liver disease present, what is the nature of the disease and what is the severity of the disease?
Further biochemical assays are often necessary when standard liver test results are abnormal. For example the measurement of bile acids is essential in the investigation of liver function during pregnancy. A full fasting lipid profile can be of help in the diagnosis of primary biliary cirrhosis, Total and pancreatic amylase levels are also important in the assessment of whether the pancreas is involved when gallstones are present. In addition to this other specialised assays play an important role in the diagnosis and monitoring of liver disease including Caeruloplasmin, Copper, Ferritin, Transferrin, Iron and Aldolase.