Ara h What? Peanut Proteins and Component Allergy Testing

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Molecular allergy component testing identifies the specific food or environmental proteins triggering a person’s allergic reactions.

Component testing can, for instance, detect exactly which peanut protein an allergic individual reacts to. So, instead of saying, “I’m allergic to peanuts,” a component-tested person could say, "I’m allergic to the Ara h 1 and 3 peanut proteins.”

The Peanut Proteins

More than 13 allergenic peanut components have been identified. The most significant for allergy detection are the proteins called Ara h 1, Ara h 2, Ara h 3, Ara h 6, Ara h 8, and Ara h 9. The designation “Ara h” comes from Arachis hypogaea, the genus and species of peanut plants.

Ara h 1, 2, and 3 are heat-resistant storage proteins frequently involved in severe peanut reactions. Up to 95 percent of those who test positive for Ara h 1, 2, or 3 experience allergic symptoms after eating peanuts, including anaphylaxis. Of these three proteins, Ara h 2 is the most frequent predictor of peanut allergy, and is more often associated with severe symptoms.

Ara h 6 is structurally similar to Ara h 2; together they account for a lion’s share of peanut allergy symptoms in the U.S.

Heat-alterable Ara h 8 proteins are correlated with cross-reactions to Birch pollen, and typically trigger only mild, localized reactions to peanuts (e.g. oral symptoms)—or none at all. Just a small percentage of those who are Ara h 8 positive report problems after peanut ingestion.

The protein Ara h 9, like Ara h 1-3, can trigger severe peanut reactions. However, most Ara h 9 allergy is in southern Europe. Those with an Ara h 9 sensitivity may also react to fruits containing pits, such as cherries, or peaches.

Component Test Benefits

The FDA first cleared molecular component blood tests for peanut allergens in 2011. Test proponents point out it provides a precise allergy assessment, similar to the way a person’s HDL and LDL cholesterol levels add precision to their total cholesterol measurement.

Component testing research also indicates:

  • Component tests reveal differences between peanut-sensitive and peanut-allergic kids that can facilitate the diagnosis of peanut allergy (helpful since most children who are considered peanut-sensitized based on standard tests do not have a peanut allergy).
  • Ara h 2/IgE blood plasma levels diagnose peanut allergy more accurately than whole peanut/IgE plasma levels.
  • Component testing can distinguish immune system peanut reactions from symptoms caused by cross-reactions to pollen proteins.
  • Peanut allergic people living in different parts of the world have different immune system and symptom patterns. Component diagnostics can help scientists and doctors understand this complexity.

Whether component testing becomes commonplace likely depends on the result of further research, and the advent of insurance coverage. For now, if the cost is not prohibitive, component testing is generally considered helpful in certain cases.

Sources: Pediatric Consultant; AAAAI; Quest Diagnostic Photo credit: Till Westermayer

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