Q. What causes a positive IgE RAST after a negative IgE tested a year ago?

Answered by
Dr. Shyam Kalyan. N
and medically reviewed by Dr. Sneha Kannan
This is a premium question & answer published on Mar 19, 2022

Hello doctor,

My test report was negative in the IgE test a year ago. Now I got a positive IgE RAST for gluten, eggs, peanut butter, and milk. What might be the cause? I have struggled with sinus issues all my life, and currently, I am taking Singular when needed and Benadryl. I was referred to an ENT specialist or allergist because of recurring sinus infections.



Welcome to

Specific immunoglobulin E (IgE) testing to allergens is not as accurate as skin prick allergy testing. It is possible to have a negative result in one and a positive in another. The factors affecting the result could be the test itself or the reagents and the lab.

I suggest skin prick allergy testing. This is the gold standard for allergy diagnosis.

The allergens you have tested positive for are all foods that are slightly less important in your condition as they are more likely to be caused by inhalant aeroallergens.

1. Have you checked sensitivities for aeroallergens for your allergy or sinus symptoms?

2. Did they check sensitivities to dust mites, cockroaches, insects, funguses, pollens, and animal dander?

Hello doctor,

Thank you for the reply.

They are not just the new immunoglobulin E (IgE) for food allergies. I eat all these foods, and I have never reacted negatively but based on this test, I am so scared to eat any of them because my doctor said it can potentially cause anaphylaxis.

It limits what I am eating. How do I find out if I am allergic for sure? And should I cut all these foods as my doctor said?



Welcome back to

Although you had all these foods till now and they did not cause any harm, it is not very sound that suddenly you turned allergic to these, and consuming them now would result in anaphylaxis which is life-threatening.

1. Till we get a final diagnosis, avoid consuming these.

2. Get tested for these substances again using the skin prick method and not via specific IgE.

3. I suggest a skin prick allergy test for these food allergens as well as the aeroallergens.

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