Gamma glutamyl transferase (GGT) is a membrane-bound glycoprotein associated with bile ducts and canaliculi. Serum increases are associated with intrahepatic bile duct obstruction and a range of biliary disease such as sporidesmin toxicity in ruminants. GGT is more useful than ALP for detecting cholestasis in large animals (horses, ruminants) due to narrower reference intervals. Glucocorticoids stimulate GGT production in dogs, similar to ALP, but anticonvulsants such as phenobarbital have only mild effects. GGT is produced abundantly by the mammary gland with high levels in colostrum (not in the horse). Neonates of most species (not cats) have high serum levels. This test has been used to assess the adequacy of colostral transfer in some species (e.g. in calves it has been suggested that levels should be >600 U/L at 1 day, >400 U/L at 3 days, >130 U/L at 5-10 days and >65 U/L at 10-15 days).

Major differentials for increased GGT include cholestasis, biliary disease, colostrum ingestion, and endocrine disease.




Plasma or Serum


Gel, plain or heparin tube

Collection protocol:

Fasted sample preferred.



Reference(s): Center, S.A. Interpretation of Liver Enzymes. In: Veterinary Clinics of North America Small Animal Practice 37:2 March 2007  p 297 – 333. Stockham, S.L and Scott, M.A. Fundamentals of Veterinary Clinical Pathology 2nd Edition 2008. Thrall M.A. Veterinary Hematology and Clinical Chemistry 2006