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Do Food Sensitivities Show Up on Allergy Testing?

Allergy testing in not completely accurate in diagnosing food sensitivities, as some triggers may produce positive results, while others may turn up falsely negative. There are varying levels of sensitivity to foods, with some people not exhibiting allergic symptoms until exposure to an increased amount of a certain food trigger. Individuals with a family history of food allergies or with preexisting allergies benefit from undergoing multiple types of allergy tests for most accurate results.

  1. Skin Prick Test

    • Skin prick tests are useful in diagnosing environmental allergens, such as dander, pollen, dust mites and mold. Food sensitivities are difficult and time consuming to diagnose, as they do not typically show up on the standard skin prick tests or may present false negatives, yet some foods allergies are relative to environmental triggers that deliver positive results. Environmental allergens determined by skin prick tests may give doctors insight as to why certain foods stimulate histamine production, leading to adverse allergic reactions in individuals.

    Cross-Reactivity

    • Pollen and mold allergies that appear positive on a skin prick test may indicate cross-reactivity, a condition in which foods related to pollen or mold species mimic seasonal allergy symptoms of allergic rhinitis, allergic asthma and oral allergy syndrome. Oral allergy syndrome is most common in people with cross-reactive sensitivities, causing tingling, burning, itching and swelling of the lips, tongue, gums and throat, resulting from contact or ingestion of foods that derive from pollinating plants or fungus, such as apples and mushrooms.

    Related Allergies/Elimination Diets

    • Mold allergies that test positive on the skin prick test may indicate aged cheese and penicillin allergies due to cross-reactivity, whereas pollinating fruits and vegetables have a cross-correlation and reactivity to pollinating trees and plants. This explains why highly sensitive people may react to fruits such as strawberries, apples and pears from pollinating trees. Elimination diets exclude possible food allergens from a patient's diet to diagnose a potential allergy in support of other diagnostic tests results, such as the skin prick test and RAST test.

    RAST Tests

    • Radio-Allergo-Sorbent Test (RAST) is a blood test administered by extracting blood from a patient and testing it against possible triggers. RAST tests measure levels of Immunoglobin E (IgE), against a potential food allergen. IgE is an antibody that responds to allergens by producing histamine, which leads to inflammation resulting in reactions. High levels of IgE in the blood can determine specific allergens as being positive, however R.A.S.T tests are not completely accurate as many food allergens go undetected due to false negative results.

    Controlled Food Challenge Tests

    • Food challenge tests are considered the most effective in diagnosing food sensitivities, however they can only be administered in allergy and immunology centers equipped with full resuscitation equipment, as anaphylaxis reactions may potentially occur. Open food challenge tests are conducted by rubbing small amounts of a potential allergen on the skin, eyes and lips, whereas double blind placebo tests provide increasing dosages of ingested allergen-filled capsules every 30 to 60 minutes. Placebo tests determine which foods cause reactions and at which dose a patient becomes intolerant of an allergen. Medical professionals observe patients for reactive symptoms throughout the testing process to pinpoint sensitivity levels.

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