RAST test

Hi everyone,

I've had allergies to pollen and dust for about 20yrs and recently had a rast blood test done in hospital, it has come back negative which is nice although I'm puzzled as I got tested for food and pet allergies and I really expected a positive result.

Not that I want it to be but I do get a reaction when I'm around certain dogs and cats and also when I eat certain meals. I've been told reactions could be minutes to up to 48hrs after contact so it's hard to pin point without tests.

Well, sometimes I get reactions straight away when I go to a house with a cat or dog and I'm coughing really bad after a lot of meals and feel like choking.

So how can a rast test be negative with all these symptoms?

I'm on fexofenadine and singulair, could that have had an influence on the test?

In the past I used to have to come off antihistamines a few days before testing so obviously I'm a bit confused.

Any ideas? I'm just fed up and want to get to the bottom of all this.

Love Lydia xx

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Normally you have to be off antihistamines and other anti-allergy meds before you have allergy test done... From what I understand the tests can come back as false negatives/positives and also depend on what allergens you have been exposed to recently...

If you where still taking anti-histamines may be worth asking to have the tests repeated.

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my Rast test to pets was ok but skin test showed a slight reaction to dogs but only slight.Grass came up with a big blister xxx

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Hi malawi2,

that's what I thought. I will investigate that, thanks.

Glynis, think you mean the prick test where they put allergens on skin and prick them with a needle? Had that done loads of times but always in the winter when I used to be off antihistamines and pollen levels low. That test has always been highly positive(all sorts of pollen).

Love Lydia xx

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You're not alone in this. I was RAST tested last year and in the past have got a negative result for things i had a positive skin prick test to. My consultant said it was a puzzle, but that he had encountered it before. I was not on antihistamines, but was on steroids.

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I've had RAST tests come back negative for things that I know cause allergy symptoms too, I was on 2 antihistamines plus steroids at the time. I've also had RAST tests done in two different hospitals within 6 weeks of each other, the first came back positive for cats whilst the second one (both times I was on steroids and antihistamines) didn't so I don't have a great deal of faith in the accuracy of the RAST tests. I've never had a reaction to my cats except when ""adventure kitty"" AKA comes home covered in all sorts of unidentified dust and crud.

The registrar I saw today at the resp clinic said that you can have RAST tests come back negative but still be allergic. I've got an appointment with immunology in a few weeks time so I'm sure I'll get some answers then.