A heterogeneous group of diseases that affect the liver and are of particular importance because of the many essential functions of the liver. It is a large organ (50–63 oz or 1400–1800 g), and it is involved in the metabolism of proteins, fats, and carbohydrates; in the production of bile and blood clotting substances; and in the metabolism and detoxification of many hormones and drugs. Because of the numerous functions of the liver, persons with liver disorders can develop a number of different signs and symptoms. One common symptom of liver disease is fatigue, although some people are entirely asymptomatic. A striking sign of liver disease is jaundice (yellowing of the skin and eyes) due to abnormal production or transport of bile. The presence of liver disease can be confirmed by performing liver function tests on the blood. Such tests can sometimes indicate the severity of the disease and occasionally even the exact type of abnormality. Usually, however, liver function tests can indicate only the presence of a liver abnormality. But a needle biopsy, in which a small amount of tissue is removed through a needle puncture for microscopic examination, can be done safely with minimal pain and inconvenience to the patient. A needle biopsy can help determine the type of liver disorder and the extent of organ damage.