Aspartate aminotransferase, or AST, is an enzyme found within various tissues throughout the body. While present in places like the heart, muscles, and kidneys, it is most notably concentrated in the liver. Measuring its level in the bloodstream is a routine procedure, performed through a common blood test. The presence of AST in the blood is a natural occurrence, but specific levels can offer insights into the health of these organs.
What is the Aspartate Aminotransferase Test?
An AST test is commonly ordered as part of a broader assessment, such as a liver function test (LFT) or a comprehensive metabolic panel (CMP). It helps detect, diagnose, and monitor potential damage or disease within the liver. When cells in organs like the liver are injured, AST can leak into the bloodstream, causing its levels to rise. Doctors use the AST test to evaluate liver health, assess the progression of existing liver conditions, monitor treatment response, or screen for liver issues in individuals with risk factors like obesity, diabetes, or a family history of liver problems.
Normal AST Ranges Across the Lifespan
Normal AST levels are measured in units per liter (U/L). These ranges vary significantly based on age and, for adults, gender. Laboratory reference ranges may differ, so always compare results against the specific range provided by the testing laboratory. Generally, AST levels tend to decrease with age in both genders.
Normal AST ranges include:
Newborns (up to 7 days old): 30 to 150 U/L for males; 24 to 150 U/L for females.
Infants (8 days to less than 12 months): 9 to 80 U/L.
Children (1 to 3 years): 20 to 60 U/L.
Children (3 to 9 years): 15 to 50 U/L.
Children (10 to 15 years): 10 to 40 U/L.
Adolescents (16 to 19 years): 15 to 45 U/L for males; 5 to 30 U/L for females.
Adults: Commonly 8 to 33 U/L, though some sources suggest up to 39 U/L. Adult women often have slightly lower ranges than men.
Factors That Can Influence AST Levels
Many factors can cause AST levels to deviate from the normal range, with elevated levels being the main concern. Liver-related conditions are common culprits, including various forms of hepatitis (viral or autoimmune), alcoholic liver disease, non-alcoholic fatty liver disease (MASLD), cirrhosis, and liver tumors. These conditions cause liver cell damage, allowing the enzyme to leak into the bloodstream.
Beyond the liver, damage to other organs containing AST can also elevate its levels. This includes muscle injury from strenuous exercise, trauma, or certain muscle diseases, as well as a heart attack or pancreatitis. Certain medications, such as statins, some antibiotics, and high doses of acetaminophen, are also known to affect AST levels. Other influencing factors include pregnancy, dehydration, and the breakdown of red blood cells.
Low AST levels are less common and typically do not indicate a significant health issue. However, they can sometimes be associated with conditions like vitamin B6 deficiency or kidney disease.
Understanding AST in Relation to ALT
Aspartate aminotransferase (AST) is frequently evaluated alongside Alanine Aminotransferase (ALT), another enzyme primarily found in the liver. While AST is present in various tissues, ALT is considered more specific to the liver, making it a stronger indicator of liver-specific damage. When liver cells are injured, both enzymes are released into the bloodstream, but their relative proportions can provide diagnostic clues.
The ratio of AST to ALT, known as the AST/ALT ratio, helps differentiate between various causes of liver injury. In most forms of liver cell injury, ALT levels tend to increase more significantly than AST, resulting in an AST/ALT ratio typically less than 1. A ratio greater than 2:1, where AST is at least twice as high as ALT, often suggests alcoholic liver disease. The ratio can also be elevated in advanced cirrhosis of any origin, or in cases of muscle injury or heart attack, due to AST’s broader tissue distribution.