Aspartate Aminotransferase

Aspartate aminotransferase (AST) is an enzyme found primarily in the liver, heart, skeletal muscle, and kidneys, though it's also present in smaller quantities in other tissues. 

Clinically, AST testing plays a pivotal role in assessing liver and heart health. When cells in these organs are damaged or inflamed, AST is released into the bloodstream, making it a valuable biomarker for detecting conditions such as liver disease, myocardial infarction (heart attack), and muscle injury. 

Understanding the testing procedure and the significance of AST levels is essential for clinicians in diagnosing and monitoring various medical conditions. 

What is AST (Aspartate Aminotransferase)?

Aspartate aminotransferase, also known as serum glutamic-oxaloacetic transaminase (SGOT), is a crucial enzyme present in various tissues throughout the body, with particularly high concentrations in the liver, heart, skeletal muscle, and kidneys. 

It plays an important role in amino acid metabolism, facilitating the conversion of aspartate and alpha-ketoglutarate into glutamate and oxaloacetate. 

While AST and ALT are both considered liver enzymes on many blood tests, elevated ALT is more specific to the liver. Elevated AST may indicate damage in other organs, such as the heart or muscle.

AST exists in two isoforms, cytoplasmic (cAST) and mitochondrial (mAST). When released into the bloodstream, the particular form of AST may offer insights into tissue-specific damage.

AST’s Role in the Body

AST is an important enzyme that plays key roles in the body. It helps in energy production by supporting the malate-aspartate shuttle, which is essential for maintaining energy balance in cells. 

AST also contributes to the urea cycle, helping detoxify ammonia and produce urea. 

In muscle and heart cells, AST aids in maintaining energy levels and proper function. 

Elevated AST levels are often seen in muscle injuries, liver damage, and heart problems, making it a useful biomarker for detecting these conditions.

Testing AST Levels

The following section outlines the testing process and interpretation of AST levels.

Test Procedure

AST is commonly ordered as part of a comprehensive metabolic panel, which includes other health and liver function biomarkers.  

The standard laboratory testing procedure for aspartate aminotransferase (AST) involves collecting a blood sample from a vein, typically in the arm. 

Fasting is not necessary for an AST test, but it is commonly ordered with other tests that recommend or require fasting.  Speak with your healthcare provider if you have questions about performing your AST test.

Reference Range for AST Levels

While reference ranges for AST are given below, it's essential to note that the specific reference range may vary slightly depending on the testing method and laboratory standards. Additionally, normal ranges differ according to age, and according to some experts, by gender.  

Reference ranges given by one medical guide include:

Adults: 0-35 units/L or 0-0.58 μKat/L (SI units) (Values tend to be slightly lower in females than males.)

Elderly: Values are slightly higher than those of other adults. 

Children:

• 0-5 days: 35-140 units/L
• < 3 years: 15-60 units/L
• 3-6 years: 15-50 units/L
• 6-12 years: 10-50 units/L
• 12-18 years: 10-40 units/L 

What Does Low Aspartate Aminotransferase Mean?

Low AST levels in the blood are relatively rare but can indicate severe liver disease, such as advanced cirrhosis or end-stage liver failure, where the liver's ability to produce enzymes is significantly compromised. 

Additionally, nutritional deficiencies, particularly in vitamin B6 (pyridoxine), which is a cofactor for AST activity, can lead to reduced enzyme levels. 

Other potential causes of low AST levels include uremia, and the use of metronidazole and/or trifluoperazine. 

What Does High Aspartate Aminotransferase Mean?

Elevated AST levels can be caused or affected by the following factors:

Causes and Risk Factors for Elevated AST Levels

Alcohol-induced liver damage: chronic alcohol ingestion and cirrhosis can elevate AST levels, typically below 300 units/L in alcoholic hepatitis.

Hepatitis: hepatitis may display a high AST:LDH ratio (>3) with AST peaking at 500−3000 units/L in acute viral hepatitis.

Other liver disease: other liver diseases like early hemochromatosis and chemical injury can also cause AST increases.

Other medical conditions: Reye syndrome can lead to elevated AST levels. 

Trauma, muscle diseases (such as dystrophy, dermatomyositis), and myocardial infarction: skeletal or cardiac muscle damage can cause AST elevation, with AST peaking around 24 hours post-infarction in the case of cardiac origin.

Various inflammatory states: pericarditis, pancreatitis, and Legionnaires' disease may increase AST levels, as can renal infarction and lung infarction.

Cholestasis: cholestasis can cause high AST levels due to the impairment of bile flow leading to hepatocellular injury and subsequent leakage of AST from damaged liver cells into the bloodstream.

Some drugs: isoniazid, phenothiazines, erythromycin, progesterone, anabolic-androgenic steroids, halothane, methyldopa, opiates, indomethacin, salicylates in children, and others, with hepatotoxicity from drugs sometimes causing elevated liver enzymes.

Acetaminophen hepatotoxicity: this can result in severe liver damage, with AST levels reaching 1960−29,700 units/L.

Understanding High AST Levels

AST elevations are understood as mild, moderate or marked. 

Mild Elevations in AST

Mild elevations in liver enzymes, such as AST, are common in clinical practice. The clinician should evaluate potential causes, as they may be the first sign of early liver damage. 
Mild elevations may be caused by:

• Fatty change in the liver
• Alcohol abuse
• Cirrhosis
• Mononucleosis
• Certain drugs

Moderate Elevations in AST

Research suggests that the most sensitive threshold for identifying acute injury lies within the moderate range of elevation, between 5 to 10 times the upper limit. 

Moderate increases are more commonly associated with acute viral hepatitis, although it may also be seen with:

• Excessive drug or alcohol use
• Certain medications
• Non-alcoholic fatty liver disease
• Cholestasis
• High vitamin A consumption

Non-hepatic origins of moderate AST increases include:

• Heart damage
• Kidney damage
• Muscle injury
• Hemolysis
• Heatstroke
• Pulmonary embolism

Marked Elevations in AST

Marked elevations in aminotransferase levels, defined as exceeding 10 times the upper reference limit, often indicate acute hepatic injury and/or tumor necrosis. Severe elevations (> 75 times the upper limit) typically suggest ischemic or toxic liver injury, 

The magnitude and rate of change in aminotransferase levels can also provide valuable initial insights into differential diagnoses. However, interpretation can be complex due to overlapping causes and varying patterns of enzyme elevation. 

Medical Conditions Associated with Elevations in AST

Drug, alcohol, medication use, and toxin exposure, should all be ruled out when elevations of liver enzymes are discovered.

Medical conditions associated with mild elevations in liver enzymes include: 

Nonalcoholic fatty liver disease: nonalcoholic fatty liver disease (NAFLD), a relatively common metabolic condition, often presents with mildly raised aminotransferase, especially in patients with metabolic syndrome and insulin resistance (although NAFLD can occur without these conditions). NAFLD is the most common cause of mild liver enzyme elevations in the Western world. 

Hepatitis: testing for hepatitis B or C infection is advisable for patients with mild elevation in aminotransferase levels, considering the high prevalence worldwide and the potential lack of specific risk factors reported by infected individuals.

Hereditary Hemochromatosis: further diagnostic considerations for mild elevations include evaluating for HFE-related hereditary hemochromatosis, characterized by iron deposition in organs.

Autoimmune hepatitis: autoimmune hepatitis should be considered in female patients with mild elevations and autoimmune disorders, with diagnosis involving autoantibody testing and liver biopsy.

Wilson's Disease: Wilson's disease may be suspected in young patients with signs of hemolysis or psychiatric/neurologic symptoms, confirmed through serum ceruloplasmin levels, copper metabolism testing, and examination for Kayser–Fleischer rings.

α-1-Antitrypsin Deficiency: α-1-antitrypsin deficiency, although more often diagnosed in childhood, should be considered in patients with pulmonary disease and elevated liver enzymes.

Celiac disease: celiac disease should be considered in patients with unexplained elevated liver enzymes, as up to 10% of such patients may have celiac disease, with diagnosis requiring tissue transglutaminase antibodies measurement and small bowel biopsy confirmation.

How to Support Healthy Aspartate Aminotransferase Levels

The following sections outline natural ways to support healthy AST levels:

Lifestyle Modifications For Reducing AST Levels

Simple diet and lifestyle interventions may help reduce elevations in AST.  

Dietary changes and recommendations:

• Reduce intake of simple carbohydrates and sugary foods and beverages.
• Focus on fruits, vegetables, whole grains, and vegetarian proteins.
• Limit alcohol consumption or avoid it altogether.
• Maintain a healthy weight through portion control and balanced meals; both obesity and metabolic impairment can negatively affect liver health.

Exercise and physical activity:

Exercise has shown beneficial effects on liver health. A combination of aerobic and strength-training exercises may be most helpful. 

Medical Interventions for Reducing AST Levels

Consult with a healthcare provider to assess the need for medications that may affect liver health, and discuss potential alternatives if necessary.

If underlying conditions such as diabetes or high cholesterol contribute to elevated AST levels, follow treatment plans to manage these conditions effectively.

Monitor liver function regularly through blood tests and follow up with healthcare providers for further evaluation and management as needed.

Importance of Further Evaluation and Management

Regular monitoring of elevated AST levels is essential for assessing liver health, guiding interventions, and implementing lifestyle changes like diet, exercise, and weight management to prevent complications.

Order AST Testing

Click here to compare testing options and order test panels that include AST.