GGT and 5′-NT

Gammaglutamyltransferase (GGT)

Located primarily in hepatocytes and to a lesser extent in a number of other organs

Highly sensitive to hepatocyte damage and cholestasis

Elevated in chronic alcohol consumption and binge drinking

Also elevated by extensive reparative processes, drugs (phenytoin and phenobarbital), obesity

Not elevated by bone disease, pregnancy, or childhood and adolescence

Used as a confirmatory test to indicate a hepatic origin for ALP elevation (GGT can be elevated in co-existing conditions, so interpret its results carefully and with consideration of the whole clinical picture)

5′ -Nucleotidase

Provides confirmation for a hepatic origin for elevated ALP similar to GGT

More specific for the liver and for cholestasis than GGT (which is generally elevated with any type of hepatocellular injury)

Controversial as to whether GGT or 5′-NT provides the best confirmatory test; in the past, 5′-NT has been more difficult to perform and thus less generally available