Aspartate Aminotransferase (AST)

What it is

Aspartate aminotransferase, often shortened to AST, is a type of protein called an enzyme. Enzymes are like tiny helpers in your body that speed up chemical reactions. AST is found in several parts of your body, but it's particularly concentrated in your liver, heart, and muscles. It plays a role in how your body uses certain amino acids, which are the building blocks of proteins.

When the cells containing AST are damaged or inflamed, some of this enzyme can leak out into your bloodstream. A blood test can measure the amount of AST circulating in your blood.

Why it matters

Because AST is released into the blood when cells are damaged, measuring its level can give doctors clues about what might be happening inside your body. If your AST levels are higher than usual, it can suggest that there's been some injury or inflammation to the cells where it's found.

While AST is present in the heart and muscles, it's also found in the liver. Therefore, elevated AST levels are often used as an indicator of potential liver problems. However, it's important to remember that AST isn't only in the liver, so a high reading doesn't automatically mean there's a liver issue. Doctors usually look at AST levels alongside other blood tests, such as alanine aminotransferase (ALT), which is more specific to the liver, and consider your overall health and symptoms.

The typical reference range for AST in the UK is usually up to 40 U/l (units per litre). This can vary slightly between laboratories.

What can cause it to be high or low

Higher than normal AST levels (AST > 40 U/l) can be associated with:

• Liver conditions: This is a common reason for elevated AST. Various liver diseases can cause inflammation or damage to liver cells, leading to AST leakage. Examples include hepatitis (inflammation of the liver, often caused by viruses like A, B, or C, or by alcohol), cirrhosis (scarring of the liver), and fatty liver disease.
• Muscle damage: Strenuous exercise, particularly activities that involve eccentric muscle contractions (like running downhill or weightlifting), can temporarily raise AST levels due to muscle cell breakdown. Injuries, muscle diseases like muscular dystrophy, or even injections into a muscle can also cause this.
• Heart conditions: Damage to heart muscle, such as during a heart attack, can release AST into the bloodstream. However, AST is less specific for heart damage than other markers like troponin.
• Other conditions: Less commonly, high AST can be linked to other issues such as haemolytic anaemia (where red blood cells are destroyed), certain medications, pancreatitis (inflammation of the pancreas), or even some cancers.

Lower than normal AST levels are generally not considered medically significant. They don't typically indicate a health problem and are usually not investigated further.

Lifestyle factors that may help

If your AST levels are high, particularly if they are linked to lifestyle factors, certain changes might be beneficial. These are things you could discuss with your GP:

• Alcohol intake: If alcohol is contributing to liver inflammation, reducing or stopping alcohol consumption can be very helpful for liver health and may help bring AST levels down.
• Diet: A balanced diet that is rich in fruits, vegetables, and whole grains, and lower in processed foods, unhealthy fats, and excessive sugar, can support overall liver function and general health.
• Exercise: While very intense exercise can temporarily raise AST, regular, moderate exercise is generally beneficial for health. It's worth discussing with your GP the right type and intensity of exercise for you, especially if you have any underlying health conditions.
• Weight management: If you are overweight or obese, losing weight can significantly improve liver health, particularly in conditions like fatty liver disease.

Questions to discuss with your GP

If you've had a blood test showing an abnormal AST level, or if you have concerns about your liver health, here are some questions you might want to ask your GP:

• What does my AST level mean in the context of my overall health?
• Are my AST levels high enough to be a cause for concern?
• Could my AST levels be related to any medications I'm taking?
• What other tests might be helpful to understand the cause of my AST level?
• Are there any lifestyle changes that could help improve my AST levels?
• What are the next steps in managing my health based on these results?