Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (939 page)

   Decreased in galactosemia

   Limitations

   Enzyme activity only may not differentiate variant form of galactosemia or carriers. For a more accurate evaluation of patients suspected to have galactosemia, the preferred test is a genetic test to identify mutation.

GAMMA GLUTAMYL TRANSFERASE (GGT)

   Definition

   The activity of this membrane-bound enzyme comes primarily from the liver. GGT is responsible for the extracellular metabolism of glutathione, the main antioxidant in cells. It is slightly more sensitive than ALP in obstructive liver disease.

   
Normal range:

   0–3 months: 4–120 IU/L

   3 months–1 year: 2–35 IU/L

   1–16 years: 2–25 IU/L

   ≥16 years: 7–50 IU/L

   Use

   To diagnose and monitor hepatobiliary disease; most sensitive enzymatic indicator of liver disease

   To ascertain whether observed elevations of ALP are due to skeletal disease (normal GGT) or reflect the presence of hepatobiliary disease (elevated GGT)