AST - Kresser Institute Membership Site

Marker Name: AST

REFERENCE RANGES FOR AST:

Laboratory reference range: 0–40 IU/L

Functional reference range:¹²

Male: 5–25 IU/L

Female: 5–23 IU/L

Please note that there are conventional sources that mention pathological indications for low ALT/AST but lab ranges still go down to zero. However, we have adjusted the functional reference range to reflect these pathological indications.

DESCRIPTION:

Aspartate aminotransferase (AST) reversibly catalyzes the transfer of an alpha amino group between aspartate and glutamate. In this conversion, α-ketoglutarate is also converted to oxaloacetate. As with other transaminases, AST requires pyridoxal 5ʹ-phosphate (vitamin B6) as a cofactor for catalysis, while the reverse reaction requires pyridoxamine 5′-phosphate.¹ AST, also known as serum glutamic oxaloacetic transaminase (SGOT), catabolizes amino acids so that they may enter the citric acid cycle and help produce energy.²

AST is found in two isozymes, one in the cytosol and the other in the mitochondria.^3,4 Cytosolic AST is found in red blood cells and heart tissue, while mitochondrial AST is found in highest concentrations in the liver. AST is also found in the skeletal muscle, pancreas, spleen, lung, kidney, and brain.⁴ In general, mild tissue injury liberates AST from the cytoplasm, while severe tissue damage additionally spills AST from the mitochondria into the serum.⁵ Currently, there is no clinical basis for distinguishing between cytosolic or mitochondrial AST in the serum.⁴

Elevated AST in the serum occurs in any disease that destroys liver cells (hepatocytes). The degree to which AST levels are increased may suggest the etiology of liver damage. Chronic liver diseases such as liver cirrhosis and chronic hepatitis result in a moderate increase in AST levels, approximately five to 10 times above the upper limit of normal.² AST levels that exceed 10 times the upper reference limit (marked elevation) usually indicate an acute hepatic injury such as liver ischemia or toxic liver injury.² Aminotransferase levels may exceed 75 times the upper limit of normal in shock liver hepatotoxic drug overdose.

Mild elevations in AST commonly occur in clinical settings.² Elevated AST may come from extrahepatic sources such as heart disease but most commonly reflects chronic alcohol use or nonalcoholic fatty liver disease.⁶ Mild serum AST excess may be due to chronic hepatitis B, hepatitis C, autoimmune disease, hemochromatosis, or abnormalities in copper metabolism (Wilson’s disease).² Since AST is present in various tissues other than liver, an elevated AST is not necessarily specific for liver damage. Vigorous exercise, skeletal muscle injury, heart muscle injury (e.g., myocardial infarction) or acute pancreatitis can raise serum AST levels.

For reasons that are not fully understood, AST levels are decreased in patients with uremia and undergoing hemodialysis.^7,8 This may be related to deficiency in vitamin B6.

AST is measured in the context of a liver function panel and GGT.⁹ ALT is higher than AST in most diseases of the liver. Infectious hepatitis or inflammatory diseases affecting the liver, for example, will elevate ALT higher than AST, making the AST/ALT ratio less than or equal to one.⁵ Conversely, alcoholic liver disease generally raises AST levels to twice that of ALT in the serum (i.e., AST/ALT ratio ≥2).¹⁰ Cirrhosis, acute bile duct obstruction, and early hepatitis will elevate AST greater than ALT in the serum.¹¹

PATHOLOGICAL/CONVENTIONAL RANGE INDICATIONS:

High in:²

Vigorous exercise
Rhabdomyolysis
Liver disease resulting in hepatocellular injury
- Liver cirrhosis
- Chronic hepatitis
- Alcoholic liver disease
- Nonalcoholic fatty liver disease
- Autoimmune hepatitis
- Acute viral hepatitis
- Hepatobiliary obstruction
- Ischemic liver injury
- Liver carcinoma
Heart muscle injury (e.g., myocardial infarction)
Acute pancreatitis
Drugs (e.g., acetaminophen, halothane)

Low in:^7,13

Vitamin B6 deficiency
Hemodialysis
Uremia

FUNCTIONAL RANGE INDICATIONS:

High in:

Metabolic dysfunction (dysglycemia, insulin resistance, etc.)
Iron overload
Nonalcoholic fatty liver disease
Viral infections
Autoimmune liver disease

Low in:

Same as conventional indications
Impaired liver function

References: