AST Blood Test: Purpose, Results & What You Need to Know

What is Aspartate Transferase (AST)?

Aspartate transferase (AST) is an enzyme that’s found in your liver, heart, pancreas, muscles and other tissues throughout your body. An enzyme is a type of protein in a cell that acts as a catalyst and allows certain bodily processes to happen. There are thousands of different enzymes throughout your body that have important functions. The AST blood test measures the amount of aspartate transferase in your blood. In most cases, your healthcare provider uses an AST blood test to help assess the health of your liver, but it can provide insight into other health conditions as well.

Understanding the AST Enzyme Function

AST catalyzes the reversible transfer of an amino group from aspartate to alpha-ketoglutarate to create oxaloacetate. This enzymatic process is essential for various metabolic functions in your body. When cells containing AST are damaged, the enzyme leaks into your bloodstream where it can be measured through a blood test. This leakage is what allows healthcare providers to detect potential damage to organs and tissues.

Why Your Doctor Orders an AST Test

The purpose of an AST blood test is to detect damage to cells. If cells in your liver are damaged, it can cause AST to leak into your blood, so an AST blood test can help find liver issues. While your healthcare provider will most often use the test to help assess liver health, an AST test can also provide information for other medical conditions and cell damage elsewhere in your body.

Common Reasons for AST Testing

Your healthcare provider may order an AST test for several reasons:

– To assess liver health as part of routine screening- To monitor an existing liver condition- To evaluate medication side effects that may affect the liver- To diagnose suspected liver disease based on symptoms- To determine if there’s muscle damage or injury- To evaluate cardiac conditions

Since AST tests are often included in routine blood panel tests that assess your general overall health, such as a comprehensive metabolic panel, you may get an AST test even if you don’t have risk factors for liver disease.

AST vs. ALT: Understanding the Difference

Alanine transferase (ALT) is an enzyme that’s commonly measured along with AST in a liver function panel or comprehensive metabolic panel (CMP). Both these enzymes can leak into your bloodstream when certain cells in your body are damaged. While both are known as liver enzymes, AST is found in more parts of your body than ALT. For this reason, higher-than-normal levels of ALT tend to be a more specific indicator of liver conditions than higher-than-normal AST levels. However, your healthcare provider will usually review both these levels together when assessing the health of your liver.

The AST-to-ALT ratio can provide additional diagnostic information. Elevated AST and ALT can be a marker of damage to tissues other than liver, particularly muscle, and especially when AST is higher than ALT. Acute muscle injury usually causes AST-ALT ratios close to or greater than 4, whereas in chronic myopathies including myositis the elevation of AST and ALT may be more symmetrical because of the shorter half-life of AST.

AST Blood Test: Preparation and Procedure

Understanding how to prepare for an AST blood test can help ensure accurate results and a smooth experience.

Fasting Requirements

If your AST test is part of a comprehensive metabolic panel (CMP), you’ll likely need to fast for 10 to 12 hours before your CMP blood test. Fasting means not eating or drinking anything other than water. It’s not as common, but if you’re only getting an AST blood test or a hepatic function panel (HFP), you don’t need to fast.

What to Expect During the Test

A phlebotomist usually performs blood draws, including those for an AST blood test, but any healthcare provider who is trained in drawing blood can perform this task. You can expect the following during an AST blood test:

– A healthcare professional will clean the inside of your arm with an alcohol wipe- A needle will be inserted into a vein to draw blood- Your blood sample will be collected in a tube- The needle will be removed and a bandage applied- The entire procedure usually takes fewer than five minutes

After your healthcare provider has collected your blood sample, they’ll send it to a laboratory for testing. There’s very little risk to having blood tests. You may have slight tenderness or a bruise at the site of the blood draw, but this usually resolves quickly.

Understanding Your AST Test Results

Once the test results are back, your healthcare provider will share the results with you. In most cases, you should have your test results within one to two business days, though it could take longer.

Normal AST Ranges

The normal range for aspartate transferase (AST) varies from laboratory to laboratory. One common reference range for an AST blood test is 8 to 33 U/L (units per liter). As ranges can vary depending on the laboratory, it’s important to check your test result report to see what your specific lab’s reference range is. The normal range for aminotransferase levels in most clinical laboratories is much lower than that for the alkaline phosphatase level.

Blood test reports, including aspartate transferase (AST) test reports, usually provide the following information:

– Your AST level- The normal reference range for your laboratory- Whether your result is within normal limits or abnormal- Any notes from the laboratory technician

Interpreting Elevated AST Levels

When considering levels of elevations, it is necessary to consider them relative to the respective upper limit of normal for each test compared. For example, consider a patient with an AST level of 120 IU/mL (normal, ≤40 IU/mL) and an alkaline phosphatase of 130 IU/mL (normal, ≤120 IU/mL). This represents a hepatocellular pattern of liver injury because the AST level is three times the upper limit of normal, whereas the alkaline phosphatase level is only marginally higher than its upper limit of normal.

Serum aminotransferase levels—ALT and AST—are two of the most useful measures of liver cell injury, although the AST is less liver specific than is ALT level. Elevations of the AST level may also be seen in acute injury to cardiac or skeletal muscle.

What Elevated AST Means

Elevated AST and ALT levels may indicate liver injury. These are the enzymes that are most commonly released into your bloodstream when your liver is stressed. As many types of liver conditions can cause AST levels in your blood to rise, healthcare providers don’t use the test alone to diagnose conditions.

Signs and Symptoms of Liver Problems

Your healthcare provider may use an AST test for diagnostic purposes when you’re experiencing signs and symptoms of possible liver problems. While healthcare providers can’t diagnose a condition based solely on AST levels, it can be an important part of the diagnostic process. Signs and symptoms of liver conditions include:

– Yellowing of the skin or eyes (jaundice)- Abdominal pain or swelling- Dark urine or pale stools- Fatigue or weakness- Nausea or vomiting- Loss of appetite

AST Testing in Blood Panels

An AST blood test is often included in a liver panel and comprehensive metabolic panel, and healthcare providers most often use it to help assess your liver health. A blood panel measures several aspects of your blood with one sample and can provide more detailed information about your overall health.

Common names for an AST blood test include:

– Aspartate aminotransferase test- SGOT (serum glutamic-oxaloacetic transaminase)- Serum aspartate transaminase

Clinical Applications and Monitoring

If you have a liver condition, your healthcare provider may order an AST test, often as part of a panel, to monitor your condition to see if it’s improving, worsening or staying the same with or without treatment. Your healthcare provider may also have you do an AST test and liver enzyme panel test if you’re taking a medication that can affect your liver.

AST in Different Clinical Scenarios

Beyond liver disease, AST can indicate damage from various conditions. Elevated AST can result from:

– Strenuous exercise- Myocardial infarction (heart attack)- Hemolysis (destruction of red blood cells)- Renal infarction- Pulmonary embolism- Muscle injury or myositis

Research has also shown that elevated AST on admission and elevated total bilirubin were independently associated with an increased risk of mortality in COVID-19 patients. Additionally, 14.8%-78% of patients with COVID-19 had abnormal alanine aminotransferase (ALT) and aspartate aminotransferase (AST) accompanied by mildly elevated bilirubin level on admission.

Frequently Asked Questions About AST Testing

Q: Do I need to fast before an AST blood test?

A: If your AST test is part of a comprehensive metabolic panel (CMP), you’ll need to fast for 10 to 12 hours before the test. However, if you’re only getting an AST blood test or a hepatic function panel, fasting is not typically required.

Q: How long does it take to get AST test results?

A: In most cases, you should have your test results within one to two business days, though it could take longer depending on the laboratory.

Q: What does a high AST level mean?

A: A high AST level can indicate damage to your liver, heart, muscles, or other tissues. However, healthcare providers use AST results along with other tests to determine the cause of elevation, as AST is not specific to liver disease alone.

Q: Is AST more specific than ALT for liver disease?

A: No, ALT is more liver-specific than AST. Since AST is found in more parts of your body than ALT, higher-than-normal levels of ALT tend to be a more specific indicator of liver conditions than higher-than-normal AST levels.

Q: Can exercise affect AST levels?

A: Yes, strenuous exercise can cause AST levels to rise due to muscle damage. If you know you’ll be having blood work done, it’s good to avoid intense exercise beforehand.

Q: Why is AST measured along with ALT?

A: AST and ALT are measured together because both enzymes can leak into your bloodstream when cells are damaged. Reviewing both levels together provides more detailed information about your liver health and helps differentiate between liver-specific and non-liver-related damage.

Q: How does the laboratory perform the AST test?

A: After the phlebotomist collects your blood sample, they send it to a laboratory where a medical laboratory scientist prepares the samples and performs the tests on machines known as analyzers.

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Sneha TeteBeauty & Lifestyle Writer

 

Sneha is a relationships and lifestyle writer with a strong foundation in applied linguistics and certified training in relationship coaching. She brings over five years of writing experience to renewcure,  crafting thoughtful, research-driven content that empowers readers to build healthier relationships, boost emotional well-being, and embrace holistic living.

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