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AST Test
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

AST Test

The AST blood test measures the levels of the enzyme aspartate aminotransferase to help diagnose liver damage or disease.

What is an AST test?

AST (aspartate aminotransferase) is an enzyme found primarily in the liver, but also in the heart, muscles, and other tissues. Under normal conditions, blood levels of AST are low. When cells containing AST are damaged, they release the enzyme into the bloodstream, causing levels to rise. This test is often performed as part of a group of liver function tests.

Why do I need an AST blood test?

You may need this test as part of a routine checkup or if you show symptoms of liver damage, such as:

  • Nausea, vomiting, or lack of appetite
  • Fatigue or weakness
  • Jaundice (yellowing of skin and eyes)
  • Abdominal pain or swelling
  • Swelling in ankles and legs
  • Dark urine or light-colored stool
  • Frequent itching

Testing is also recommended for those with a history of liver disease, alcohol use disorder, obesity, diabetes, or those taking medications that may cause liver damage.

What happens during an AST blood test?

A health care professional will draw a small blood sample from a vein in your arm. The procedure takes less than five minutes.

Will I need to do anything to prepare for the test?

You may need to fast (no food or drink) for up to 12 hours before the test, as it is often ordered alongside other blood work. Inform your provider of all medications you are taking, but do not stop taking them unless instructed to do so.

Are there any risks to the test?

There is very little risk, with only a slight chance of pain or bruising at the puncture site.

What do the results mean?

Low levels of AST are generally considered normal. High levels may indicate liver damage or other conditions, including:

  • Hepatitis or cirrhosis
  • Mononucleosis
  • Heart problems or procedures
  • Pancreatitis
  • Hemochromatosis
  • Deep burns or seizures
  • Liver toxicity due to alcohol or medication use

Because results can be influenced by pregnancy, exercise, age, sex, and medications, consult your provider to interpret what your specific levels mean.

Is there anything else I need to know?

Providers often order an ALT (alanine transaminase) test alongside the AST test. Elevated levels of both enzymes are strong indicators of liver damage.

Frequently Asked Questions

Most labs recommend fasting for 8–12 hours before a liver panel that includes AST, especially if the test is ordered with a fasting glucose or lipid panel. Water is usually allowed. If you’re on medication that requires food, discuss with your provider; otherwise, skip meals and avoid alcohol, caffeine, and nicotine for the recommended period.
high AST level indicates that cells containing the enzyme—most often liver cells—have been damaged. Clinicians compare AST to ALT (alanine aminotransferase) because ALT is more liver‑specific. A higher AST/ALT ratio (often >2) suggests alcohol‑related liver injury or heart muscle damage, while a ratio <1 points more toward viral hepatitis or non‑alcoholic fatty liver disease. The absolute values, trend over time, and clinical context guide diagnosis and management.
Yes. Drugs such as statins, acetaminophen (high doses), certain antibiotics (e.g., isoniazid), and anti‑epileptics can raise AST. Some supplements (e.g., high‑dose vitamin A, anabolic steroids) also affect levels. Inform your provider of all prescription, over‑the‑counter, and herbal products before testing.
Results are typically available within 24–48 hours. If your AST is elevated, your clinician will review your medication list, alcohol use, and symptoms, and may order additional tests (e.g., imaging, hepatitis serology). Follow up appointments are scheduled to interpret the results and plan treatment or lifestyle changes.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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