Thank you for your inquiry.
I am not aware of any test to detect allergy glycerin and could find no testing procedure in the literature other than that used for contact dermatitis. The reference for this is:
Preston PW and Finch TM. Allergic contact dermatitis from glycerin in a moisturizing cream. Contact Dermatitis 2003 (October); 49(4):221-222.
I think application to the skin (as for contact urticaria or contact dermatitis) would be the only valid way to test to this substance since it is irritating upon injection. The only other way to test your patient would be a provocative challenge, which you could perform using the glycerin suppositories themselves.
Thank you again for your inquiry and we hope this response is helpful to you.
Phil Lieberman, M.D.