When do you know that your liver has been damaged?

Generally you don't : Most liver diseases are asymptomatic until advanced cirrhosis occurs. Some subtle symptoms include diffuse itching, yellow eyes or skin, abdominal swelling, confusion and sleep disturbance, loss of muscle mass in the arms and legs. Liver disease can generally be detected earlier by labwork or a good physical exam.

Liver damage : Depends on severity and cause of liver damage. It can be mild, moderate or severe. The person would have nausea, vomiting , weakness, malaise, yellow skin, clay stool, orange yellow urine , weight loss, abdominal pain, enlarged liver and abnormal liver function tests and serological tests. Thanks.

Liver function tests: You would need to get liver function tests (blood test), which include ast, alt, alkaline phosphatase, bilirrubin, albumin. Also other proteins such as coagulation factors reflect how the liver is working. An ultrasound of the liver is a good starting imaging study to assess the liver.