Because the liver performs so many vital jobs, liver diseases can have serious consequences. Death occurs if the liver stops functioning. In some cases of advanced liver disease, physicians can remove the patient's damaged liver and replace it with a healthy liver from a deceased donor.

Most liver diseases are painless in their early stages and therefore are difficult to detect. In many cases, one of the earliest signs of liver disease is jaundice. Jaundice occurs when the blood contains an excessive amount of bilirubin. This excess bilirubin causes a yellowish discoloration of the skin and the whites of the eyes. Jaundice may result if diseased liver cells fail to remove bilirubin from the blood. Jaundice also may occur if gallstones block the common bile duct, thus preventing the excretion of bilirubin in the bile.

Hepatitis is an inflammation of the liver. Hepatitis may be caused by viruses or by toxins. There are five main types of viral hepatitis: hepatitis A, B, C, D, and E. They are spread in different ways and have different characteristics. For example, hepatitis A usually spreads through food and water that have been contaminated by human or animal waste. Most cases do not result in serious illness. Hepatitis B is transmitted by close contact with an infected person, or by exposure to infected blood. Severe cases of hepatitis B can lead to liver failure and death. A vaccine that prevents hepatitis B is available, and public health experts in the United States recommend that all children be vaccinated against this disease.

Toxic hepatitis results from exposure to various chemicals. Such substances include carbon tetrachloride and other cleaning fluids, industrial chemicals, and certain medications.

Cirrhosis occurs when scar tissue replaces healthy liver cells. This process decreases the ability of the liver to perform its vital functions. Cirrhosis ranks as the sixth leading cause of death in the United States. However, not all cases of cirrhosis result in death. Alcoholism is the most common cause of cirrhosis. Hepatitis can also cause cirrhosis.

Other liver diseases. Because the liver filters disease-causing microorganisms from the blood, it frequently becomes infected when diseases strike other parts of the body. Such diseases as tuberculosis, amebic dysentery, histoplasmosis, and syphilis--all of which begin elsewhere in the body--can eventually affect the liver. Cancers from other parts of the body also often spread to the liver.

Charles S. Lieber, M.D., Professor of Medicine and Pathology, Mount Sinai School of Medicine, City University of New York. -