Your routine blood test results are in, and you see 'Aspartate Aminotransferase' listed. What does it mean for your health?
Understanding your blood test results can sometimes feel like deciphering a foreign language. One of the labs commonly included in "standard" routine lab panels is aspartate aminotransferase, abbreviated AST. Included in the broader category of liver enzyme tests, this protein can offer insights into liver and metabolic health, potentially indicating issues before clinical symptoms appear.
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What Is Aspartate Aminotransferase (AST)?
AST is a type of protein called an enzyme that helps speed up chemical reactions involved in the metabolism of amino acids, which are the building blocks of proteins. Specifically, AST helps convert an amino acid called aspartate into oxaloacetate, which cells require to make energy. Sometimes, you may also see AST referred to as serum glutamic-oxaloacetic transaminase (SGOT).
AST is found in multiple locations throughout the body, including:
- Liver
- Heart
- Skeletal muscles
- Kidneys
- Pancreas
Measuring small amounts of AST in the blood is normal when these tissues are healthy. However, if injury or inflammation occurs within any of these tissues, they will leak AST into the bloodstream, resulting in higher-than-normal blood levels.
Normal AST Levels
The standard reference range for AST levels in adults is between 8 to 30 units per liter (U/L). However, this range can vary slightly depending on the laboratory and factors like the individual's age, sex, and weight.
Why Is Aspartate Aminotransferase Tested?
AST is included in a blood test called a comprehensive metabolic panel (CMP). This test is often part of a general health screening to assess blood sugar, electrolyte balance, kidney health, and liver function. Tracking even small changes in these biomarkers over time helps doctors catch and correct potential health problems before they manifest as clinical diseases.
Additionally, doctors may order AST as part of a more focused medical evaluation to assist in diagnosing, monitoring, and managing various health conditions, including:
- Liver disease
- Heart conditions
- Kidney disease
- Muscle injury
- Pancreatitis
- Hemolytic anemia
- Alcohol abuse
- Medication side effects
Because AST is most commonly associated with liver health, it is frequently included in liver function tests within a liver panel. Doctors may order this test if you exhibit signs and symptoms of liver disease, such as:
- Fatigue
- Muscle weakness
- Yellowing of the skin and eyes (jaundice)
- Right upper abdominal pain
- Nausea and vomiting
- Loss of appetite
- Dark urine
- Light stools
- Easy bleeding and bruising
- Itchy skin
- Swelling in the feet, hands, face, or abdomen
- Unintentional weight loss
Elevated AST Levels – What Do They Mean?
AST is a non-specific marker, meaning many different things can cause its levels to rise. Generally, higher AST levels suggest that cells in the body are injured, but they don't show exactly where the injury is or what caused it.
Therefore, abnormal AST results should always be reviewed by a qualified healthcare professional. Doctors will look at other lab results and consider the patient's medical history to understand the bigger picture. Additional tests are usually needed to confirm the AST elevation and to identify its underlying cause.
AST elevations can be classified as mild, moderate, or severe based on the degree of elevation:
- Mild: 2-5 times the upper limit of normal
- Moderate: 5-15 times the upper limit of normal
- Severe: > 15 times the upper limit of normal
Note: These classifications may vary depending on specific laboratory standards and clinical guidelines.
Causes of Elevated AST
Mild elevations may be attributed to:
- Medication use
- Alcohol use
- Liver cirrhosis
- Metabolic dysfunction-associated steatotic liver disease (MASLD) (formerly called non-alcoholic fatty liver disease [NAFLD])
- Chronic hepatitis B and C infections
- Autoimmune hepatitis
Moderate and severe elevations of AST may indicate:
- Acute exacerbations of chronic liver diseases
- Drug-induced liver injury
- Ischemic liver injury (loss of blood flow to the liver)
- Biliary tract obstruction (e.g., gallstones)
- Liver cancer or tumors
AST can also rise due to non-liver-related causes. According to one study, the most common non-hepatic causes of marked AST elevations could be categorized into skeletal muscle damage, heart muscle damage, and hematologic (blood) disorders.
More specifically, examples of non-hepatic causes of high AST include:
- Muscle injury or disorders
- Heart attack
- Blood cancers
- Hemolytic anemia (increased red blood cell destruction)
- Hemochromatosis
- Wilson disease
- Pancreatitis
- Mononucleosis
- Alpha-1 antitrypsin deficiency
- Celiac disease
Elevated AST levels do not always indicate a medical condition. Certain factors can temporarily raise AST levels in the absence of disease, including:
- Deep burns
- Recent seizure
- Heart procedures or other surgery
- Intense exercise
- Pregnancy
- Taking certain medications or supplements
AST vs. ALT – What's the Difference?
AST is rarely measured in isolation. Instead, it is often measured alongside other tests to provide a more complete picture of health status and narrow down the source of abnormal results.
Comparing AST and ALT
Alanine aminotransferase (ALT) is another liver enzyme commonly measured with AST as part of a liver panel or CMP. ALT is considered a more direct and specific indicator of liver health than AST because it is found in fewer other tissues.
If ALT levels are normal but AST levels are high, it could indicate a health problem outside the liver.
Conversely, if both AST and ALT levels are elevated, it could indicate a liver-related problem. The AST/ALT ratio is sometimes used by healthcare providers as a diagnostic tool to help identify underlying liver diseases:
- AST/ALT Ratio > 2: May suggest alcoholic liver disease
- AST/ALT Ratio < 1: May indicate chronic hepatitis and non-alcoholic steatohepatitis (NASH)
Note: These ratios are part of a broader diagnostic process and should be interpreted by qualified healthcare professionals.
How to Manage Abnormal AST Levels
If your AST test result is abnormal, your doctor will likely order additional tests to help determine the reason and recommend various treatments to support liver health.
Diagnostic Follow-Ups
Additional liver tests may include:
- Blood tests to measure other liver enzymes, proteins, and blood clotting functions
- Viral hepatitis panel
- Autoimmune liver panel
- Imaging of the liver via ultrasound, CT scan, or MRI
- Elastography to measure the level of fibrosis (hardened tissue) in the liver
- Liver biopsy
Treatment and Lifestyle Adjustments
Treatment recommendations for high AST levels depend on the underlying cause. Fortunately, less than 5% of people with elevated liver enzymes have serious liver disease, meaning lifestyle modifications may be enough to normalize AST levels.
Dietary and lifestyle modifications that may help lower liver enzymes include:
- When clinically relevant, weight loss via lifestyle changes has the most supporting evidence for improving liver enzyme levels.
- Avoid drinking alcohol
- Eat a balanced, healthy diet rich in antioxidants, sulfur compounds, and omega-3 fatty acids, and limit processed foods rich in saturated fats and added sugars.
- Talk to your doctor about alternative medication options if you are taking a drug that can increase liver enzymes. These include, but are not limited to, acetaminophen, NSAIDs, statins, and amiodarone.
- Exercise regularly, incorporating aerobic and resistance training into your routine.
Always consult with a healthcare professional before making significant lifestyle or medication changes.
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Key Takeaways
- An AST blood test measures the amount of aspartate aminotransferase in the blood.
- AST is primarily found in the liver, heart, muscles, kidneys, and pancreas. While AST is commonly categorized as a liver enzyme, elevated levels can indicate damage or injury to any of these organs.
- Measuring AST with other tests, such as ALT, can help determine if a liver condition is likely contributing to abnormal results. However, to definitively diagnose liver disease, your doctor will order additional blood and imaging tests.
- Adopting a healthy lifestyle, such as eating a nutritious diet, exercising regularly, and moderating alcohol intake, can support liver health and prevent liver enzyme elevations.
- If you have concerns about your AST levels or overall liver health, consult your physician for personalized advice and ensure you undergo regular health screenings.