Peanut Allergy: Advances in Diagnosis and Treatment
It is estimated that food allergy affects approximately 5% of adults and 8% of children, with peanut allergy nearing approximately 2% of the population. A peanut allergy is when the immune system makes a type of antibody called IgE towards specific proteins in peanut. When a person with peanut allergy is exposed to these peanut proteins, the peanut specific IgE antibodies cause allergy cells (mast cells, basophils, eosinophils, etc.) to create an allergic reaction. The symptoms of an IgE mediated allergic reaction generally happen within minutes to two hours after exposure to the food and can include: itching, flushing, hives, swelling, difficulty breathing, repeated coughing, chest tightness, wheezing, hoarseness, change in voice, dizziness, weakness, fainting, low blood pressure, nausea, vomiting, abdominal cramps, or diarrhea. Such reactions can be life threatening.
The history of a previous reaction is one of the most important diagnostic tools in determining if an IgE mediated food allergy is present. If the history is consistent with an IgE mediated food allergy (timing and symptoms), then further testing may be needed to confirm this allergy, or to determine if a patient has grown out of their food allergy. The gold standard for food allergy diagnosis is an oral food challenge, which is when the food thought to cause an allergic reaction is given to the patient in a medical facility in small increments and increased until either an allergic reaction occurs, or a serving size is reached. Realistically, however, this is mainly performed to rule out a food allergy, and is performed if the likelihood of having an IgE mediated food allergy reaction is low. In order to determine the likelihood of an IgE mediated food allergy the following tests are available: specific IgE towards peanut, peanut component testing to proteins in peanut (Ara h 1, 2, 3, 8 and 9), and skin prick testing. Screening with panels of different food IgE’s without a previous history of a reaction to that food is poorly informative, and should not be done for routine evaluation of allergy. This is because a positive serum food specific IgE test may show sensitization, but not necessarily clinical allergy. This is an important distinction because a patient may have an elevated serum IgE to a food and have no allergic reaction when eating this food.
Skin prick testing is usually done first, as it is a less invasive test. Sometimes specific serum IgE to peanut is also obtained to determine the likelihood of IgE mediated peanut allergy. The level that is considered to be associated with a clinical allergy is different for each food. Peanut component testing may also be helpful. This looks at the specific IgE levels of different peanut proteins. If the Ara h 8 level is elevated, this is associated with less likelihood of a clinical allergy to peanut, whereas elevated IgE levels to Ara h 1, 2, and 3 are associated more with clinical allergy. It is important to have a board certified allergist evaluate these tests and determine if an oral food challenge is warranted.
The current approach to managing peanut allergy is avoidance and treating allergic reactions promptly and appropriately. However, there are ongoing trials to investigate the potential of treating peanut allergy. The most promising trials include: Oral Immunotherapy (OIT), Sublingual Immunotherapy (SLIT), Epicutaneous Immunotherapy (EPIT), and a Chinese herbal formula. OIT has been studied the longest (more than 10 years) and has shown both short term and longer-term responses to therapy. However, it does have its limitations due to safety issues. In one trial, after receiving 4g of peanut for 5 years through OIT, 50% of subjects passed an oral food challenge and were able to re-incorporate peanut into their diets. The most limiting side effect from OIT is that 10-15% experience gastrointestinal symptoms that prevent the continuation of therapy. Other more severe symptoms have also been reported. SLIT is similar to OIT, but smaller doses of allergen are administered under the tongue. This has been shown to have fewer side effects than OIT. In one study, after 44 weeks of therapy, 70% of patients were able to consume 5g of peanut powder, or at least 10-fold more peanut powder than at baseline. EPIT uses delivery of peanut allergen to the skin, called a peanut patch. A large study is currently ongoing for the peanut patch in the United States and Europe. No safety concerns have been noted after 11 months of EPIT. A Chinese herbal formal is also being investigated that has shown no significant side effects.
Peanut allergy diagnosis and determining if a patient has out-grown this allergy can be difficult and requires specialized training from a board certified allergist. At Allergy Partners, all of our physicians are board certified or eligible allergists and we stay up to date with the latest in diagnostics and treatment.