What is the AST blood test?
An 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.
Common names for an AST blood test include:
→ Aspartate transferase (AST).
→ Aspartate aminotransferase (AST).
→ Serum glutamic-oxaloacetic transaminase.
→ Aspartate transaminase.
What is Aspartate transferase (AST)?
Aspartate transferase (AST), also known as aspartate aminotransferase, is an enzyme that exists in your liver, heart, brain, pancreas, kidneys, muscles and many tissues in your body. Although it can be found throughout your body, AST is most commonly associated with liver health. When cells that contain AST are damaged, they release the AST into your blood.
What are enzymes?
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.
Why test AST?
When your cells get damaged, AST can leak into your bloodstream. Because of this, high levels of AST in a blood sample can be a sign of an underlying medical condition — most often (but not always), a liver condition. An AST blood test measures the amount of AST in your blood. The test is commonly used to help diagnose liver damage or disease.
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. An AST blood test is most often included in a blood test panel, such as a liver enzyme panel (HFP) or a Comprehensive Metabolic Panel (CMP). A blood panel measures several aspects of your blood with one sample and can provide more detailed information about your overall health.
Why do I need an AST blood test?
You may get an AST blood test as part of your routine checkup (see CMP) or if you have symptoms of liver damage.
These liver damage symptoms may include:
→ Nausea and vomiting
→ Lack of appetite
→ Jaundice, a condition that causes your skin and eyes to turn yellow
→ Swelling and/or pain in your abdomen (belly)
→ Swelling in your ankles and legs
→ Dark-colored urine (pee) and/or light-colored stool (poop)
→ Frequent itching
Even if you don't have symptoms, your health care provider may order an AST blood test if you're more likely to develop liver disease because of:
→ A family history of liver disease
→ Alcohol use disorder
→ Taking certain medicines that can cause liver damage
→ Hepatitis or exposure to hepatitis
AST and your liver:
Your liver is an organ that has many important jobs:
→ It makes a fluid called bile that helps your body digest food.
→ It also removes waste products and other toxins from your blood.
→ It produces proteins, as well as substances that help your blood clot.
Alcohol or drug use and diseases such as hepatitis can damage your liver and keep it from doing these jobs.
AST is an enzyme your liver makes. Other organs, like your heart, kidneys, brain, and muscles, also make smaller amounts. AST is also called SGOT (serum glutamic-oxaloacetic transaminase).
Normally, AST levels in your blood are low. When your liver is damaged, it puts more AST into your blood, and your levels rise.
A high AST level is a sign of liver damage, but it can also mean you have damage to another organ that makes it, like your heart or kidneys. That's why doctors often do the AST test together with tests of other liver enzymes.
When cells become damaged, AST can be released into the bloodstream. For this reason, abnormal levels of AST in a blood sample can indicate an underlying problem.
Although AST can be measured alone, it is usually included with other enzymes as part of broader tests, such as a liver panel or comprehensive metabolic panel (CMP). When interpreted alongside other enzymes, an AST measurement can help identify liver disease and other health issues.
To understand the significance of your results, your doctor often looks at AST and the levels of other enzymes included in a liver panel test. Patterns in which enzymes are normal or abnormal can offer meaningful clues about an underlying problem.
Because AST levels in the blood can rise when cells are damaged, elevated AST can reflect health conditions, including liver diseases like cirrhosis or hepatitis. To determine the cause of an abnormal result, the doctor may consider how high the AST level is and how it compares to the levels of other liver enzymes.
Very high levels of AST often reflect short-term liver damage, while smaller but persistent elevations in AST over time can be tied to chronic conditions. However, because AST is found in other body parts, it can be elevated in the blood due to cell damage outside the liver.
For this reason, the doctor may look at the levels of both AST and the enzyme alanine aminotransferase (ALT) side by side. ALT is more concentrated in the liver, so if AST is high while ALT is normal, it can indicate a problem outside the liver. In other cases, though, having a much higher level of AST than ALT can be a sign of alcohol-induced damage to the liver.
It is also important to note that having elevated AST is not proof of a medical problem. If you are healthy with proper liver function, you may still have an AST level outside the normal range, which can occur based on individual factors like age, sex, race, diet, exercise, or having taken medications that can affect AST.
What is the normal range for an AST blood test?
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.
It’s also important to know that there’s no AST range that’s normal for all people. A healthy AST level can change depending on several factors, including:
→ Your age.
→ Your sex.
→ Your race.
→ Your weight.
AST levels are usually listed on your test report in units per liter (U/L) or international units per liter (IU/L). Next to the level found in your blood, the test report should list the laboratory’s reference range.
It is important to look closely at the range for the specific lab that analyzed your sample because there is no universal reference range for AST. Ranges can vary because not all labs use the same methods, and studies have not demonstrated a precise healthy range.
In addition, no AST level is normal for all people. Instead, a healthy AST level can change depending on your age, sex, race, weight, and other factors that your doctor can consider when interpreting your test result.
If your results are not in the normal range, it doesn't always mean that you have a medical condition that needs treatment. Many things can affect your results, such as certain medicines and your age, sex, and diet.
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Low AST levels may indicate:
→ Vitamin B6 deficiency
→ Kidney disease
→ Liver disease
→ Autoimmune conditions
→ Genetic condition
An elevated AST level may be a sign of a liver condition. Liver disease is even more likely when the results of other liver blood tests are also abnormal. Although it’s not as common, elevated AST levels can be caused by cell damage in other areas of your body as well.
A high AST level may indicate any of the following liver conditions:
→ Alcohol-induced liver injury.
→ Hepatitis (liver inflammation).
→ Cirrhosis (scarring of the liver).
→ Taking medications that are toxic to your liver.
→ Liver tumor or liver cancer.
→ Liver ischemia (not enough blood flow to your liver, which leads to death of liver tissue).
A high AST level may also indicate any of the following conditions that aren’t directly related to your liver:
→ Hemochromatosis (having too much iron in your body, which damages your heart, liver and pancreas).
→ Heart attack (myocardial infarction).
→ Mononucleosis ("mono").
→ Muscle disease.
Your AST levels can also increase temporarily after the following events:
→ Deep burns.
→ Heart procedures.
→ Intense exercise.
People who are pregnant may also have increased levels of AST.
Should I be worried if I have a high AST test result?
If your AST test result is higher than the given normal range on your report, it doesn’t necessarily mean that you have a medical condition that needs treatment. People with healthy and proper liver function can have an AST level outside of the normal range, which can happen due to several factors, including:
→ Your age.
→ Your sex.
→ Your race.
→ Your diet.
→ Taking medications that can affect your AST levels.
→ If you’re pregnant.
Do I need follow-up tests if my AST results are abnormal?
Your healthcare provider may recommend follow-up tests if you have an abnormal AST level.
Follow-up testing may include:
→ Repeat AST blood tests.
→ Other blood tests.
→ Imaging tests.
→ A biopsy.
Some diseases or medicines you take can cause a “false positive” result on the AST test. This means your test is positive, even though you don't have liver damage. Any of these can cause a false positive result:
→ Diabetic ketoacidosis (Your body can’t make enough insulin, which helps sugar enter your cells.)
→ Some antibiotics, such as erythromycin estolate or para-aminosalicylic acid (Paser)
Levels of both aspartate aminotransferase (AST) and alanine aminotransferase (ALT) may increase with strenuous exercise, and hospital admission has been observed to induce a 5% increase in AST levels (0.4%–9.6%, 95% confidence interval [CI]) and a 17.5% increase in ALT levels (9.1%–21.6%, 95% CI) in healthy subjects; restricted physical activity and hospital diet have been suggested as possible explanations for these increases.
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