Percentage of false positives and false negatives w RAST

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VintageMom
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by VintageMom on Tue Feb 21, 2012 8:05 pm

Percentage of false positives and false negatives w RAST

How often to false positives and false negatives occur with the RAST food allergy blood test? When a retest is done several months later, will the same false results appear, or is there a chance an entirely new set of false results may crop up?
Last edited by VintageMom on Wed Feb 22, 2012 8:43 pm, edited 1 time in total.

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Dr Adam Fox
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by Dr Adam Fox on Wed Feb 22, 2012 12:13 am

Re: Percentage of false positives and false negatives w RAST

RAST (or specific IgE tests) are reliable when interpreted carefully in the context of a clinical history. They simply can't be used a 'yes' or 'no' tool to tell you what you are allergic to. As mentioned in a previous response, it is key that they are interpreted by a doctor with appropriate experience at doing so.
Dr Adam Fox
MA(Hons), MD, MSc, MB, BS, DCH, FRCPCH, FHEA, Dip Allergy

http://www.talkhealthpartnership.com/on ... am_fox.php

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mark
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Location: Hampshire
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by mark on Wed Feb 22, 2012 12:40 pm

Re: Percentage of false positives and false negatives w RAST

delayed reactions are easily missed. would you agree the Elise test followed by ACT/ DTH would be a good way to track down the culprits?
Mark Westbrook
Fitness Consultant
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Dr Stephen Till
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by Dr Stephen Till on Wed Feb 22, 2012 1:20 pm

Re: Percentage of false positives and false negatives w RAST

As far as I am aware such tests are not used in our routine clinical practice.
Dr Stephen Till
Consultant in Adult Allergy, Guy's and St Thomas' NHS Foundation Trust

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mark
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by mark on Wed Feb 22, 2012 3:01 pm

Re: Percentage of false positives and false negatives w RAST

oh ok what would you suggest as a good journey to source the culprits.
Mark Westbrook
Fitness Consultant
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Dr Helen Brough
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by Dr Helen Brough on Wed Feb 22, 2012 7:18 pm

Re: Percentage of false positives and false negatives w RAST

Dear Mark,

Specific IgE tests are not good at testing for delayed allergies as these are not usually IgE mediated. They are usually T cell mediated. The same goes for skin[ prick tests. There are some tests for delayed allergies including patch testing for food (although there is conflicting evidence on this). For contact allergies such as nickel and other chemicals patch testing is much more reliable. Delayed intradermal testing is sometimes used for delayed reactions to drugs but not for foods.

In paediatrics (which is what I mainly practice) most of the delayed allergies for foods giving to rise to gastrointestinal symptoms or eczema are assessed by removing the considered offending food from the diet strictly for 4-6 weeks followed by reintroduction. This most by done under dietetic supervision.

Kind regards,
Dr Helen Brough
Consultant in Paediatric Allergy
Guy's & St. Thomas' NHS Foundation Trust

http://www.talkhealthpartnership.com/on ... brough.php

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