I looked in an old (1988)  "Laboratory Diagnostic Tests" by Frances
Fischbach, but they don't present the numbers the way you show it (your
library may be able to find a more recent copy).  I also saw there is a bunch
of information when doing a google search (keywords:  lab test GGT).
Apparently, there are a whole bunch of reasons why the GGT could be elevated
including some medications.  If you have your lab sheet, it should show a
range of normal values inside brackets; you really need to compare your
number with what the numbers inside the brackets show.  I don't know how they
perform a GGT or if all labs use the same methods or use the same number
value system.  In other words, I don't know if that number would be the same
in another lab.

The lab book I used, which is not current, indicates values can be increased
in liver diseases, alcohol consumption, gall bladder problems, pancreatitis,
and with a lot of drugs/medications.  They also said it is generally
increased in men because of the large amounts of this enzyme found in the
prostrate.

There is another small section in the book that says why this test is used
for monitoring a wide range of drugs (like if the patient is actually taking
the drug and so on).

Barb