Is there a blood test to determine if you are allergic to soy?

Yes: There is a test called leap; uses blood to check for allergies to foods in every category. It works by measuring leukocyte responses to the food adn can show even subtle allergies. I use this in my practice and it has been a big help for many people with migraines, irritable bowel syndrome, hypertension, diabetes, Crohn's and many others.

Yes: Yes, but skin testing is much more sensitive. A blood test is more likely to miss a soy allergy than skin testing. See an allergist.