Gamma-glutamyltransferase
Introduction of GGT
The highest concentration of GGT is found in the cells of the renal tubules but, as it is excreted in the urine, levels do not rise in response to renal damage. Circulating enzyme is considered to originate from the liver (biliary epithelial cells and hepatocytes) and, as with ALP, levels increase in response to cholestasis. GGT is found lower in the biliary tree than ALP but is not specific in differentiating hepatocellular from cholestatic disease. In the dog, steroid induction of GGT occurs but it is less influenced by barbiturate therapy and may be useful in monitoring therapy and screening for barbiturate induced hepatopathy. GGT is considered a specific indicator of hepatobiliary disease in the cat.
Small Animals
Causes of increased GGT activity
- Glucocorticoid therapy (dog)
- Cholestasis
- Hepatobiliary disease
Complementary tests
ALP (increases in ALP largely parallel those in GGT in the dog, but in cats GGT increases may be greater than ALP). ALT and GLDH, bile acids and bilirubin.
Equine
GGT is considered a specific indicator of both acute and chronic hepatobiliary disease. GGT has a long half life and levels may remain elevated after the pathology resolves.
Causes of increased GGT activity
- Mild to moderate increases with obstructive disease of the large colon but may increase with gastrointestinal disease of any nature particularly if recurring
- Cholestasis
- Acute and chronic liver failure
- Secondary to hepatocellular damage in hepatobiliary disease, chronic hepatic insufficiency and after hepatotoxic insult (for example, Ragwort poisoning)
- Higher in younger animals and in young horses in training
Complementary tests
AST and GLDH, bile acids and bilirubin.