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A family member had a blood test called IgG to check for any delayed allergies. It showed milk and eggs to be a severe, but delayed allergy (no skin reaction). Is there a blood test that can check if she has a delayed allergy to other birds’ eggs (i.e. turkey, duck, quail, etc.) and other animals’ milk (i.e. goat milk, sheep milk, or maybe unpasteurized raw cow milk, etc.)?
In IgG testing, the blood is tested for IgG antibodies instead of being tested for IgE antibodies (the antibodies associated with food allergies). IgG is a “memory antibody”. 

When you have a blood test to query response to an immunization, this is also IgG testing. A common example is a “Rubella titer.” 

In the context of food, IgG signifies memory through exposure to a food.  Because a normal immune system should make IgG antibodies to foreign proteins (to include foods), a positive IgG test to a food is a sign of a normal immune system, and suggests tolerance or “memory” of the food rather than food allergy.  Therefore, IgG testing is not recommended for evaluation of food allergies.

If the patient has previously eaten the food (milks, eggs), he or she would likely have IgG to the food.