GGT and alcohol intake

• Gamma-glutamyltransferase (GGT) is a membrane-bound glycoprotein enzyme
  • catalyzes the transfer of the gamma-glutamyl moiety of glutathione to various peptide acceptors
  • chronic ethanol consumption is known to readily induce a rise in serum GGT
    • there is a positive correlation between ethanol intake and serum GGT activity
      • the WHO/ISBRA collaborative project on markers of alcoholism indicated elevated serum GGT concentrations in 52% of alcohol-dependent subjects (1)
      • the sensitivity of GGT as an alcohol marker has usually shown to be higher for men than for women (1)
  • due to the lack of specificity, GGT is a poor marker when alcohol consumption needs to be screened in patients with non-alcoholic liver diseases or in hospitalised patients
    • GGT is increased in all forms of liver disease, particularly in cases of intra- or posthepatic biliary obstruction
      • small increases (2-5 times normal) are observed in fatty liver
  • in alcoholics, serum GGT may help to distinguish those with or without liver disease
    • interpretation of GGT with respect to ALT and AST
      • raised level of GGT must be interpreted in the context of other liver function tests (2)
        • mild liver disease tends to result in a ratio of alanine transaminase (ALT) to aspartate transaminase (AST) of greater than 1 and therefore with an AST of 30 and an ALT of 60, a patient with a non-alcoholic fatty liver would have a raised GGT
        • more extensive liver disease tends to result in an ALT to AST ratio of less than 1 and therefore a raised GGT with an AST of 70 and an ALT of 30 is compatible (but not diagnostic of) alcohol damage
        • in a patient who is known to abuse alcohol; if the AST and ALT are normal then the GGT may provide an indicator of recent alcohol intake
  • alcohol cessation and relation to GGT
    • increased activities usually return to normal if the patient abstains from alcohol with a normalization time of 2-3 weeks
    • helping to distinguish those with or without liver disease and relationship to normalization of GGT
      • persistently abnormal values in the absence of continuing ethanol exposure suggest liver disease, typically when GGT is initially 8-10 times normal and if the elevation persists after 6-8 weeks of abstention from alcohol (1)
      • if initial GGT levels are only 2-3 times normal and return to normal after abstention, the patient is likely to be devoid of liver disease (1)

Reference:

• (1) Niemela O. Biomarkers in alcoholism Clinica Chimica Acta 2007; 377: 39-49
• (2) Pulse (2002), 62 (16), 84.