Page 3 - Project

Laboratory Testing

Allergy laboratory testing measures circulating allergen specific IgE, which is formed
after an initial priming exposure to an allergen. Not all allergen specific IgE laboratory
methods are alike because allergen sources and technologies differ. Some methods
use recombinant purified allergen because they are less expensive to produce.
Allermetrix uses purified natural allergens because recombinant allergens are not
identical to the natural allergens, and may not react exactly like the natural peanut
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allergens . The Allermetrix quantitative method uses liquid allergens which preserve
the natural conformation of proteins unlike solid phase allergen systems that cause
significant denaturation of the allergen proteins. Sensitivity of the liquid allergen
method is much better than solid phase systems because of very low background
binding that cannot be accomplished with solid phase systems. Allermetrix uses the
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WHO 2 IRP IgE primary calibrator and the lowest non-zero calibrator (0.04 kU/L),
which corresponds to the concentration for an equivocal positive result. Solid phase
systems use much higher positive calibrators (e.g. 0.35 kU/L) and extrapolate to zero.

When testing for peanut allergy using peanut specific IgE, positive results do not
always correspond to clinical peanut allergy. Peanut has allergens that cross-react
with a wide variety of other allergen sources that can result in a positive blood test
when the patient has grass, tree, weed, or other food allergies. In a recent report from
NHANES (National Health and Nutrition Examination Survey) 2005-2006 several
allergen specific IgE measurements were performed on a cross sectional sample of
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the US aged 6 and up . Each person answered a standardized questionnaire and was
categorized as non-allergic, having current allergies, or as having current hay fever.
Individuals with high levels of peanut specific IgE were much more likely to have
current hay fever, suggesting there is strong cross-reactivity between peanut and
many pollen allergens.

Allermetrix investigated the in-vitro response of patients who presented with clinical
signs of peanut allergy and compared them to samples that were from atopic and non-
atopic individuals. Each sample was tested for specific IgE to Peanut, Ara h 1, Ara h
2, and a set of known and potential cross-reactants: timothy and alfalfa grass; acacia,
mesquite and birch tree; ragweed and mugwort pollens; English walnut, black walnut,
soybean, hazelnut, brazil nut, almond, and cashew nut; and peach. Each sample was
also assayed for total IgE. As in the previous studies, allergen specific IgE to Ara h 2
was best correlated with clinical peanut allergy.

Laboratory testing to aid identification of “true” peanut allergy should include total IgE
and specific IgE to the following allergens: peanut, Ara h 1, Ara h 2, timothy grass,
river birch, mugwort, brazil nut, walnut, cashew, pistachio, chestnut, pecan nut,
sesame seed, hazelnut, and peach.

Ara h 1 and Ara h 2 are both associated with peanut allergy. In many studies, Ara h 2
has been demonstrated to be most closely associated with “true” peanut allergy 1,4,5,6,7 .
Ara h 1 has also been shown to be associated with “true” peanut allergy 1,4,6 .
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