I recently received blood results showing gamma globulin levels of 0.37 when normal range is 0.7-1.6. is it possible that this is a one-time thing?

Maybe: Reference ranges are set so that several percent of healthy folks fall outside on either side. This may just be you. It is no danger. Stop worrying. If this continues or you are very curious, you can get the various types quantitated. Some folks run way-low on one of the three major types. Usually they still do okay.

Yes: particularly if you have not had recurrent or difficult to eradicate infections. low IgG can be due to immune deficiency, various non-immune conditions or lab error. next step is to recheck, then see Immunologist if the low value is repeated. it is possible to have low antibody levels with a normal functioning immune system, but it could also be a clue toward identifying a treatable condition