Liver Disease

Overview of the Liver

The liver is a vital organ located in the upper right-hand side of the abdomen. Somewhat larger than the size of a football and weighing about 2-3 pounds, 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 metabolizing 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 moves from these small ducts into larger ones, like streams into a river, eventually traveling into the common bile duct and out of the liver. Some of the bile flows directly to the duodenum; the rest is stored and concentrated in the gallbladder. After a person eats, the gallbladder, a fist-sized organ that sits next to the liver, releases some of the stored bile into the small intestine, where it helps to digest fats.

What is liver disease?

Liver disease is categorized both by the cause and the effect it has on the liver. Causes may include infection, injury, exposure to drugs or toxic compounds, an autoimmune process, or a genetic defect (such as hemochromatosis). These causes can lead to hepatitis, cirrhosis, stones that develop and form blockages, fatty liver, and in rare instances liver cancer. Genetic defects can prevent vital liver functions and lead to the deposition and build-up of damaging substances, such as iron or copper.

Laboratory Tests

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. Some 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
Gamma-glutamyl transferase (GGT) – an enzyme found mainly in the liver; very sensitive to changes in liver function

2. Bilirubin: Bilirubin, a waste product made from old or damaged 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:

Total bilirubin - measures all the bilirubin in the blood
Direct bilirubin - measures a form conjugated (combined with another compound) 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 ordered together, these tests may be called a liver panel.

Other tests may be ordered to help diagnose the cause of liver dysfunction. These may include:

Specific hepatitis tests [see Hepatitis A, Hepatitis B, Hepatitis C] - to detect viral hepatitis
Complete blood count (CBC) - to evaluate the patient’s white and red blood cells and platelets
Prothrombin time (PT) – to evaluate clotting function
Alfa-fetoprotein (AFP) – may be elevated with liver cancer
Tests for iron status - when hemochromatosis is suspected
Liver biopsy – a tiny sample of liver tissue is taken to evaluate the structure and cells of the liver

Non-Laboratory Tests

Computerized axial tomography (CAT) scan
Ultrasound