Ken,

IgE (immunoglobin E) are antibodies that develop when a body 
becomes sensitized to an allergy such as a food.  IgE levels
can be determined by a blood test.

Some allergies result in production of IgE antibodies and the
reactions are called IgE mediated food allergies, others 
allergies do not result in the development of IgE and
are called non-IgE mediated response.

IgE mediated allergies are usually the ones resulting in 
hives, eczema and anaphylaxis,
whereas the non-IgE mediated ones are limited to the 
digestive symptoms (abdominal pain, nause, vomiting, 
diarrhea, etc.)

IgE mediated food allergy is testable by RAST testing 
(blood test) or skin  testing.

This is my understanding of it in layman's terms based upon 
what I have heard and what I have read.

Lynda