Liver Blood Enzymes
How Are Healthy People Evaluated For Mild To Moderate Rises In Aminotransferase Levels?
Evaluation of healthy patients with abnormal liver enzymes needs to be individualized. A doctor may ask for blood test data from old records for comparison. If no old records are available, the doctor may repeat blood tests in weeks to months to see whether these abnormalities persist. The doctor will search for risk factors for hepatitis B and C including sexual exposures, history of blood transfusions, injectable drug use, and occupational exposure to blood products. A family history of liver disease may raise the possibility of inherited diseases such as hemachromatosis, Wilson’s disease, or alpha-1- antitrypsin deficiency.
The pattern of liver enzyme abnormalities can provide useful clues to the cause of the liver disease. For example, the majority of patients with alcoholic liver disease have enzyme levels that are not as high as the levels reached with acute viral hepatitis and the AST tends to be above the ALT. Thus, in alcoholic liver disease, AST is usually under 300 units/liter while the ALT is usually under 100 units/ liter.
If alcohol or medication is responsible for the abnormal liver enzyme levels, stopping alcohol or the medication (under a doctor’s supervision only) should bring the enzyme levels to normal or near normal levels in weeks to months. If obesity is suspected as the cause of fatty liver, weight reduction of 5% to 10% should also bring the liver enzyme levels to normal or near normal levels.
If abnormal liver enzymes persist despite abstinence from alcohol, weight reduction and stopping certain suspected drugs, blood tests can be performed to help diagnose treatable liver diseases. The blood can be tested for the presence of hepatitis B and C virus and their related antibodies. Blood levels of iron, iron saturation, and ferritin (another measure of the amount of iron stored in the body) are usually elevated in patients with hemachromatosis. Blood levels of a substance called ceruloplasmin are usually decreased inpatients with Wilson’s disease. Blood levels of certain antibodies (anti- nuclear antibody or ANA, anti-smooth muscle antibody, and anti-liver and kidney microsome antibody) are elevated in patients with autoimmune hepatitis.
Ultrasound and CAT scan of the abdomen are sometimes used to exclude tumors in the liver or other conditions such as gallstones or tumors obstructing the ducts that drain the liver.
Liver biopsy is a procedure where a needle is inserted through the skin over the right upper abdomen to obtain a thin strand of liver tissue to be examined under a microscope. The procedure is oftentimes performed after ultrasound study has located the liver. Not everybody with abnormal liver enzymes needs a liver biopsy. The doctor will usually recommend this procedure if 1) the information obtained from the liver biopsy will likely be helpful in planning treatment, 2) the doctor needs to know the extent and severity of liver inflammation/damage, or 3) to evaluate the effectiveness of treatment.
Liver biopsy is most useful in confirming a diagnosis of a potentially treatable condition. These potentially treatable liver diseases include chronic hepatitis B and C, hemachromatosis, Wilson’s disease, autoimmune hepatitis, and alpha-1-antitrypsin deficiency.
How About Monitoring Aminotransferase Levels?
What is usually most helpful is serial testing of AST (SGOT) and ALT (SGPT) over time to determine whether the levels are going up, staying stable, or going down. For example, patients undergoing treatment for chronic hepatitis C should be monitored with serial liver enzyme tests. Those responding to treatment will experience lowering of liver enzyme levels to normal or near normal levels. Those who develop relapse of hepatitis C after completion of treatment will usually develop abnormal liver enzyme levels again.
What About Other Liver Enzymes?
Aside from AST and ALT, there are other enzymes including alkaline phosphatase, 5’-nucleotidase (“5 prime” nucleotidase), and gamma-glutamyltranspeptidase (GGT) that are often tested for liver disease.
We have restricted this consideration of liver enzymes to AST and ALT because they are biochemically related to each other and, more importantly, they are the two most useful liver enzymes.