Is there an DNA test to detect a wheat allergy?

No. At least, not yet. There are other ways to detect wheat allergy. This involves identifying the presence of ige antibodies specific for wheat. This can be accomplished with skin testing or a blood test called rast. Both tests are good - neither is superior to the other; they complement each other. Studies show that IgG antibodies indicate protection against wheat & other food allergies.
Wheat allergy. There are several types of blood tests and also skin tests that allergist do to diagnosis wheat allergy.