The AST blood test, also called the aspartate aminotransferase test, measures the level of an enzyme found mainly in the liver, heart, and muscles. It helps doctors evaluate how well the liver is working and identify possible damage caused by conditions like hepatitis, cirrhosis, or heart problems.
When liver cells are injured, AST levels in the blood increase, which can indicate acute or chronic liver disease, alcohol-related injury, or medication effects. The test is often ordered together with the ALT test and other liver function tests to better understand the cause and severity of enzyme changes.
Treatment depends on the underlying cause of high AST levels, such as managing fatty liver, stopping certain medications, or reducing alcohol use. A doctor may also recommend lifestyle changes, additional blood tests, or imaging exams to monitor liver health and prevent complications.
When is AST ordered?
The AST blood test may be ordered by a doctor when it is necessary to assess liver health, particularly in patients who are overweight, have a history of fatty liver, or show signs or symptoms like yellow skin, pain in the right side of the abdomen, pale stool, or dark urine.
This test can also be ordered to assess this enzyme in people taking medications that can damage the liver and to assess the liver health of people who consume excessive alcohol.
Normal levels
The normal range for AST varies depending on sex, age, and the methods used by the laboratory. The following table summarizes typical reference values (in U/L) used in the United States.
AST levels above 1000 U/L generally indicate severe liver injury, such as ischemic hepatitis, drug-induced liver damage (especially from acetaminophen), or acute viral hepatitis.
High AST levels
Because the AST blood test is not specific, your doctor may order this test together with other liver tests, such as gamma-glutamyl transferase (GGT) and alkaline phosphatase (ALK).
A high AST level may be a sign of:
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Acute pancreatitis
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Acute viral hepatitis
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Alcoholic hepatitis
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Liver cirrhosis
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Liver abscess
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Primary liver cancer
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Major trauma
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Illicit drug use
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Heart failure
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Ischemia
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Infarction
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Burns
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Hypoxia
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Obstruction of the bile ducts, such as cholangitis or choledocholithiasis
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Muscle damage
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Hypothyroidism
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Use of drugs such as heparin, salicylates, opiates, tetracycline, thorazine, or isoniazid
Values above 150 U/L usually indicate liver damage, while levels above 1000 U/L may indicate drug-induced hepatitis or ischemic hepatitis, for example. On the other hand, low AST values can indicate a vitamin B6 deficiency in the case of people who need dialysis.
AST vs ALT: What’s the difference?
AST (aspartate aminotransferase) and ALT (alanine aminotransferase) are both enzymes used to evaluate liver health, but they differ in where they are found in the body and what they indicate.
ALT is mainly found in the liver, making it a more specific marker for liver injury. AST is found in several organs, including the liver, heart, muscles, and kidneys. Because of this, an elevated AST level alone is less specific for liver damage and may indicate muscle or heart problems.
AST is present both in the cytoplasm and mitochondria of cells, while ALT is primarily in the cytoplasm. This means that AST can increase more during severe or chronic liver injury involving extensive cell death, such as cirrhosis or alcoholic liver disease.
Together, AST and ALT provide complementary information that helps determine the type and severity of liver or other tissue damage.
De Ritis ratio (AST/ALT ratio)
The De Ritis ratio, or AST/ALT ratio, is used to help determine the cause and severity of liver injury. It compares the amount of AST to ALT in the blood and provides diagnostic clues about the type of liver condition.
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A ratio less than 1 is typical of viral hepatitis, non-alcoholic fatty liver disease (NAFLD), or mild hepatocellular injury.
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A ratio between 1 and 1.5 may indicate developing fibrosis in chronic liver disease.
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A ratio greater than 2 is strongly suggestive of alcoholic liver disease, due to mitochondrial AST release and vitamin B6 deficiency.
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A ratio greater than 1 in non-alcoholic conditions can also indicate the onset of cirrhosis.
This ratio is often evaluated along with other markers, such as GGT and alkaline phosphatase, to identify the specific pattern and cause of liver injury.
How to lower AST levels
AST levels can often improve when the underlying cause is treated or managed through lifestyle and dietary changes.
What foods, exercises, and medications impact AST
Regular physical activity helps lower AST levels, particularly in people with non-alcoholic fatty liver disease (NAFLD). At least 150 minutes per week of aerobic exercise, such as brisk walking or swimming, can reduce inflammation and improve liver enzyme levels.
A balanced diet plays an important role in supporting liver health. The Mediterranean diet, rich in fruits, vegetables, fish, olive oil, and whole grains, is associated with significant reductions in AST. Weight loss of 5–10 % of body weight also improves liver enzyme levels and decreases fat accumulation in the liver.
Certain foods and nutrients may specifically help reduce AST:
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Coffee: Regular coffee consumption is linked to lower AST and ALT levels due to its antioxidant properties.
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High-fiber foods: Fruits, vegetables, and whole grains help eliminate toxins from the body.
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Folate-rich foods: Leafy greens, beans, eggs, and dairy products support liver function.
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Cruciferous vegetables: Broccoli, kale, and cabbage contain compounds that help detoxify the liver.
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Nuts and omega-3-rich fish: Help lower triglycerides and improve liver enzyme balance.
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Vitamin E and curcumin: These antioxidants may help lower AST in people with non-alcoholic fatty liver disease.
Avoiding alcohol and hepatotoxic medications is essential for lowering AST levels. Drugs such as acetaminophen, certain antibiotics, and some herbal supplements can increase liver enzymes. People with liver disease should consult a doctor before taking any new medication.
Stress management, maintaining a healthy weight, and regular monitoring of liver function tests are also key strategies for keeping AST levels within a normal range.