Aspartate Aminotransferase (AST)

What is AST?

Aspartate Aminotransferase (AST) is an enzyme that is important for amino acid metabolism. It’s found in various tissues throughout the body. The widespread presence of AST, especially in vital organs like the liver and heart, underlines its importance in routine health assessments.

While both AST and ALT (alanine aminotransferase) are enzymes related to liver function, AST’s presence in the heart, kidneys, brain, and muscles sets it apart. This broader distribution means that elevated AST levels can indicate issues beyond liver damage, including heart conditions or muscle damage. Therefore, AST levels are often evaluated alongside ALT levels to get a more comprehensive view of liver health and to help pinpoint the source of tissue damage.

Why is AST important?

AST’s significance lies in its ability to signal tissue damage. Elevated levels of AST in the blood can indicate liver damage, as with ALT, but can also suggest problems in other organs, particularly the heart. This makes AST a versatile marker for assessing overall health and diagnosing specific conditions.

Monitoring AST levels can aid in diagnosing conditions such as hepatitis, cirrhosis, and heart diseases. It also plays a crucial role in evaluating the severity of diseases and the effectiveness of treatments, offering a broader perspective on one’s health status.

How can I better understand my AST results?

AST test results are typically expressed in units per liter (U/L), similar to ALT. The “normal reference” ranges can vary by laboratory but are generally in the range of:

• Adults: ~13 to ~39 units per liter (U/L). The
  • “normal” reference range for women is often lower than for men.

It’s important to understand that these “normal” ranges are based on average values from a specific population, and it is hard to know the general health of this population that was used to come up with the “normal” range. Factors such as age, gender, race, and even muscle mass can influence AST levels. Therefore, the population used to develop these ranges might not align with your specific health profile or goals. In general, lower is typically better.

For instance, slightly elevated AST levels could be considered normal for some individuals, depending on various health and lifestyle factors. Conversely, a result within the “normal” range doesn’t always guarantee a perfectly healthy liver. It’s also important to consider other liver enzyme tests, like ALT (Aspartate Aminotransferase), and the overall clinical context.

Where can I learn more?

• Cleveland Clinic: AST
• Medscape: AST
• Kalas, MA, et al. 2021. Abnormal liver enzymes: A review for clinicians