Aspartate transaminase (AST) is an enzyme produced in the liver. It plays an important role in amino acid metabolism. It is normally found in the liver, heart, muscles, brain, kidneys, and red blood cells.

The level of AST in the blood is often tested to reveal the presence of liver disease or of damage to the liver.

The test for AST is normally conducted in conjunction with other tests, especially for alanine tranaminase (ALT) and for alkaline phosphatase (ASP).

Elevated AST

Normal serum AST is 14-20 IU per liter in men and 10-36 IU per liter in women. When a blood test for AST indicates elevation above normal range, the indication is that damage may be present to one of the organs where AST is normally found.

Elevated AST can be an indicator of liver disease, heart and cardiovascular disease, damage to the skeletal muscles, severe burns, severe loss of blood, acute renal (kidney) failure, acute pancreatitis, diseases of the muscles or the skeletal system, or serious injury of any kind. High AST levels can also be produced by some types of cancer, recent ingestion of high amounts of vitamin A, mononucleosis, and as a side effect of a long list of medications, including statins (anti-cholesterol medication), many antibiotics, chemotherapy, large doses of aspirin, barbiturates, and opioid drugs (narcotics).

If ALT is also found to be elevated, the presence of liver disease is more strongly indicated. In that case, elevated AST can help to identify the cause. If the elevation of AST is higher than that of ALT, this is a strong indicator that the damage to the liver is alcohol-related.

Because AST can be elevated due to a long list of causes, both pathological and non-pathological, an AST test is always best used in conjunction with other diagnostic tests that can help to pinpoint the actual cause of the test result. AST is commonly measured along with other enzymes as part of the standard diagnostic liver function test.

Liver Disease

When elevated AST indicates damage to the liver, this damage can come from a variety of different causes, both in the sense of indicating various liver diseases and also in the sense of the diseases being due to various causes. Diseases of the liver that can produce elevated AST levels range from fatty liver disease (which is relatively harmless in itself and normally asymptomatic, but still a cause for concern because
it may represent an early stage of something more serious), to potentially life-threatening illnesses such as cirrhosis of the liver or liver cancer. Other liver diseases that can produce elevated AST include hepatitis, liver fibrosis, and non-cancerous liver tumors.

Of the causes of liver disease, probably the single most common culprit (although not responsible for the majority of cases) is alcohol abuse. Drinking large amounts of alcohol over time can cause any of the liver diseases above with the possible exception of liver cancer. Alcoholic liver disease produces higher elevation of AST than non-alcoholic liver disease in most case.

Other causes of liver disease include obesity, diabetes, genetic and hereditary factors, and viral and bacterial infections such as viral hepatitis. When a combination of blood tests including but not limited to a test for elevated AST shows likely damage to the liver, further diagnostic procedures are indicated. These normally include the use of medical imaging technology such as an ultrasound or a CT scan, inquiry into the patient’s diet, lifestyle, body weight, and medical history, and may include a liver biopsy to confirm certain diseases such as cancer, cirrhosis, or infectious hepatitis.

Many liver diseases are progressive and the damage from them is irreversible. When the damage becomes severe, prognosis is poor and fatality becomes likely, although a successful liver transplant can extend the patient’s life for years in extreme cases. For this reason, early detection of liver disease is extremely important.

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