Overview of the Liver
The liver is a vital organ located in the upper right-hand side of the abdomen. It performs numerous functions for the body: converting nutrients derived from food into essential blood components, storing vitamins and minerals, regulating blood clotting, producing proteins and enzymes, maintaining hormone balances, and metabolising and detoxifying substances that would otherwise be harmful to the body. The liver also makes factors that help the human immune system fight infection, removes bacteria from the blood, and makes bile, which is essential for digestion.
Bile, a greenish-yellow fluid consisting of bile acids (or salts) and waste products, such as bile pigments, flows through small bile ducts inside the liver. The bile flows from these small ducts into larger ones, like streams into a river, eventually leading to the common bile duct. The cystic duct connects the common bile duct to the gallbladder. After eating, the gallbladder, an organ that sits next to the liver and stores bile, releases bile into the small intestine where it helps to digest fats.
Liver disease is often discovered during routine testing. It may not cause any symptoms at first or the symptoms may be vague, like weakness and loss of energy. In acute liver disease, most commonly symptoms related to:
- problems handling bilirubin, including jaundice (yellowing of the skin and eyes), dark urine, and light stools
- loss of appetite
- nausea
- vomiting
- diarrhoea
Chronic liver disease symptoms may not be present until the disease has reached an advanced stage. They include:-
- jaundice, dark urine
- abdominal swelling due to the accumulation of fluid (ascites)
- pruritus (itching)
- unexplained weight loss or gain
- abdominal pain
Three types of tests are often used to detect liver disease; these tests either measure the levels of specific enzymes, bilirubin, or protein present in the test sample (usually a blood sample). Among the more common tests in these three categories are:
1. Enzymes: Enzymes are proteins that help cells do their work. When cells are injured, enzymes can leak into the blood at higher-than-normal levels. Three common enzymes used to detect liver disease are:
- Alanine aminotransferase (ALT) – an enzyme found mainly in the liver; the best test for detecting hepatitis
- Alkaline phosphatase (ALP) – an enzyme related to the bile ducts; often increased when they are blocked
- Aspartate aminotransferase (AST) – an enzyme found in the liver and a few other places, particularly the heart and other muscles
2. Bilirubin: Bilirubin, a waste product made from old blood cells, is a yellow compound that causes jaundice and dark urine when present in increased amounts. Two different tests of bilirubin are often used together, especially if a person has jaundice:
- Total bilirubin - measures all the bilirubin in the blood
- Conjugated bilirubin - measures a form made in the liver
3. Protein: One of the main functions of the liver is to make protein. Two important liver tests include:
- Albumin - measures the main protein made by the liver and tells how well the liver is making this protein
- Total Protein - measures albumin and all other proteins in blood, including antibodies made to help fight off infections (antibodies are not made in the liver)
Doctors often use these tests together to tell whether liver damage has occurred and how severe it is. When requested together, these tests are called liver function tests.
More specialised blood tests for liver disease may be requested by the doctor in addition to the tests above to investigate or monitor specific liver conditions. These tests are referred to within the individual sections on liver disorders on this site.