AST (SGOT) and ALT (SGPT) are sensitive indicators of liver damage from different types of disease. But it must be emphasized that
higher-than-normal levels of these liver enzymes should not be automatically equated with liver disease. They may mean liver problems or they may not. The interpretation of elevated AST and ALT levels depends upon the whole clinical picture and so it is best done by doctors experienced in evaluating liver disease.
The precise levels of these enzymes do not correlate well with the extent of liver damage or the prognosis (outlook). Thus, the exact levels of AST (SGOT) and ALT (SGPT) cannot be used to determine the degree of liver disease or predict the future. For example,
patients with acute viral hepatitis A may develop very high AST and ALT levels (sometimes in the thousands of units/liter range). But most patients with acute viral hepatitis A recover fully without residual liver disease. For a contrasting example, patients with chronic hepatitis C infection typically have only a little elevation in their AST and ALT levels. Some of these patients may have quietly developed chronic liver disease such as chronic hepatitis and cirrhosis (advanced scarring of the liver).
The highest levels of AST and ALT are found with disorders that cause the death of numerous liver cells (extensive hepatic necrosis). This occurs in such conditions as acute viral hepatitis A or B,
pronounced liver damage inflicted by toxins as from an overdose of acetaminophen (brand-name Tylenol), and prolonged collapse of the circulatory system (shock) when the liver is deprived of fresh blood bringing oxygen and nutrients. AST and ALT serum levels in these situations can range anywhere from ten times the upper limits of normal to thousands of units/liter.
Mild to moderate elevations of the liver enzymes are commonplace. They are often unexpectedly encountered on routine blood screening tests in otherwise healthy individuals. The AST and ALT levels in such cases are usually between twice the upper limits of normal and several hundred units/liter.
The most common cause of mild to moderate elevations of these liver enzymes is fatty liver. In the United States, the most frequent cause of fatty liver is
alcohol abuse. Other causes of fatty liver include
diabetes mellitus and obesity. Chronic hepatitis C is also becoming an important cause of mild to moderate liver enzyme elevations.
A host of medications can cause abnormal liver enzymes levels. Examples include:
Pain relief medications such as aspirin, acetaminophen (Tylenol), ibuprofen (Advil, Motrin), neproxen (Narosyn), diclofenac (Voltaren), and phenybutazone (Butazolidine)
Anti-seizure medications such as phenytoin (Dilantin), valproic acid, carbamazepine (Tegretol), and phenobarbital
Antibiotics such as the tetracyclines, sulfonamides, isoniazid (INH), sulfamethoxazole, trimethoprim, nitrofurantoin, etc.
Cholesterol lowering drugs such as the "statins" (Mevacor, Pravachol, Lipitor, etc.) and niacin
Cardiovascular drugs such as amiodarone (Cordarone), hydralazine, quinidine, etc.
Anti-depressant drugs of the tricyclic type
With drug-induced liver enzyme abnormalities, the enzymes usually normalize weeks to months after stopping the medications.
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.
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Liver Enzimes and Atkins
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