The AST blood test, or aspartate aminotransferase test, is a blood test that is ordered to investigate for liver injury and evaluate functioning in the presence of liver diseases such as hepatitis or cirrhosis.
AST is an enzyme present in the liver. It is usually elevated when liver damage is more chronic, as it is located more internally in the liver cell. However, this enzyme can also be present in the heart and can be used as a cardiac marker, indicating infarction or ischemia.
As a liver marker, AST is usually measured together with ALT, since it can be elevated in other situations and is non-specific for this purpose. The normal level of AST is between 5 and 40 U/L of blood, although this reference range can vary depending on the laboratory. This enzyme may also be referred to as the TGO or oxalacetic transaminase.
High AST levels
Because the AST blood test is not specific, your doctor may order this test together with other liver tests, such as gamma-glutamyl transferase (GGT), and alkaline phosphatase (ALK).
A high AST level may be a sign of:
- Acute pancreatitis
- Acute viral hepatitis
- Alcoholic hepatitis
- Liver cirrhosis
- Liver abscess
- Primary liver cancer
- Major trauma
- Illicit drug use
- Heart failure
- Obstruction of the bile ducts, such as cholangitis, choledocholithiasis
- Muscle damage
- Use of drugs such as heparin, salicylates, opiates, tetracycline, thorazine or isoniazid
Values above 150 U/L usually indicate liver damage, while levels above 1000 U/L may indicate drug-induced hepatitis or ischemic hepatitis, for example. On the other hand, low AST values can indicate a vitamin B6 deficiency in the case of people who need dialysis.
De ritis ratio
The de Ritis ratio is used in medical practice to assess the extent of liver damage and determine the best treatment approach. This ratio takes into account the AST and ALT values. The ratio, when higher than 1, may be a sign of more serious liver injury, such as cirrhosis or liver cancer, for example. When it is lower than 1, it may indicate an acute phase of viral hepatitis, for example.
When is AST ordered?
The AST blood test may be ordered by a doctor when it is necessary to assess liver health, particularly in patients who are overweight, have a history of fatty liver, or show signs or with specific symptoms like yellow skin, pain in the right side of the abdomen, pale stool or dark urine.
This test can also be ordered to assess this enzyme in people taking medications that can damage the liver and to assess the liver health of people who consume excessive alcohol.