ALT - Kresser Institute Membership Site

Marker Name: ALT

REFERENCE RANGES FOR ALT:

Laboratory reference range: 0–44 IU/L

Functional reference ranges:¹⁸

Male: 5–26 IU/L

Female: 5–20 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:

Alanine aminotransferase (ALT), formerly called serum glutamate-pyruvate transaminase (SGPT),¹ is an enzyme found predominantly in hepatocytes that catalyzes the transfer of an amino group from alanine to alpha-ketoglutarate, yielding pyruvate and glutamate. Serum ALT levels are routinely measured to detect and characterize diseases of the liver.²

ALT is a sensitive and somewhat specific indicator of liver cell injury.³ While the highest activity of ALT is in the liver, lesser amounts can be detected in skeletal muscle and kidney.⁴ ALT is found exclusively in the cytoplasm and spilled into the bloodstream when cells are injured.⁵ Thus, virtually any disease that destroys hepatocytes will increase serum levels of ALT.⁶ Aminotransferases are cleared from the circulation by sinusoidal cells in the liver.⁷ While the half-life of ALT in the circulation is approximately two days, massive liver injury may cause prolonged ALT elevations.³

An elevated level of ALT in the serum may manifest before clinical symptoms of liver disease. When interpreting serum ALT levels, it is important to use age- and gender-specific reference limits; normal values of ALT in men are 25 to 30 percent higher than they are in women of the same age.^8,9

The extent of ALT elevations in the blood may provide a clue to the etiology of liver damage. The causes of liver injury from highest serum ALT elevation to lowest are as follows: ischemic or toxic liver injury, acute viral hepatitis, autoimmune hepatitis, alcoholic liver disease, chronic hepatitis, and liver cirrhosis.⁷ The rate and degree to which ALT increases and subsequently returns to normal also varies by etiology. Acute ischemic hepatitis causes extremely high increases in serum ALT with a relatively rapid return to normal. On the other hand, acute viral hepatitis rises more slowly and does not usually reach the same levels as would occur in acute ischemic hepatitis. Likewise, serum levels of ALT return to normal relatively slowly in acute viral hepatitis compared to ischemic liver injury.⁷

Aminotransferase levels, including ALT, are abnormally low in patients on hemodialysis.¹⁰ This is likely, but not necessarily, due to vitamin B6 deficiency.¹¹ Abnormally low ALT levels, in isolation, are not usually a cause for concern.^3,7

ALT is measured with aspartate aminotransferase (AST) as part of a standard liver function panel.¹² Examining the ratio of AST to ALT can provide some additional clues to the mechanism of hepatic injury. ALT is higher than AST in most diseases of the liver, such as viral or autoimmune hepatitis.¹³ On the other hand, alcoholic liver disease, liver cirrhosis, acute bile duct obstruction, and early hepatitis will elevate AST greater than ALT in the serum.^14,15 Gamma-glutamyl transpeptidase (GGT) is also routinely measured with ALT and may be superior to AST and ALT levels in detecting alcohol abuse or alcoholic liver disease.^16,17

PATHOLOGICAL/CONVENTIONAL RANGE INDICATIONS:

High in:^7,19

Muscle injury (e.g., rhabdomyolysis)
Hypervitaminosis A
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
Renal cell injury
Hemolysis
Drugs and toxins (e.g., acetaminophen, halothane, carbon tetrachloride, lead)

Low in:^10,11,20

Vitamin B6 deficiency
Hemodialysis

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: