Peanut Allergy Awareness

The mean patient age for a diagnosis of peanut allergy is about 14 months; only 20% of the patients diagnosed with a peanut allergy (most likely those with a baseline peanut-specific serum IgE level 18) will outgrow it by the time they reach school age.^18,20 Those who do should be encouraged to consume peanuts on a regular basis; according to Byrne et al,²¹ 8% of patients with allergy resolution experience recurrence, a possible result of infrequent peanut consumption.

PHYSICAL EXAMINATION
Patients with peanut allergies can present with a range of symptoms, possibly involving cutaneous, cardiovascular, gastrointestinal, and/or respiratory systems (see Table 1^15,22). The more notable symptoms, possibly developing within 15 minutes of exposure, are progressive upper and lower respiratory difficulties, vomiting, diarrhea, hypotension, edema of the face and hands, arrhythmia, throat tightness (in serious cases, approaching anaphylaxis), and possibly loss of consciousness. Such severe reactions often occur in the child who has ingested raw peanuts or tree nuts.²²

Milder physical exam findings include erythema, pruritus, conjunctivitis, abdominal pain, nasal congestion, itchy throat, and sneezing. These reactions may have been triggered by foods produced in a facility that also processes nuts, household utensils used to prepare foods that contain nuts, or cross-contamination from another child.^9,15,24

DIAGNOSTIC WORK-UP
The diagnosis of a patient with a peanut allergy is made through thorough history taking, careful physical examination, allergy testing with either a skin prick test (SPT) or serum-specific IgE, and oral food challenges. The gold standard for diagnosing food allergy is the double-blind, placebo-controlled oral food challenge,^2,25-27 as this test alone can determine the amount of peanut protein needed to trigger a reaction in the given patient.⁹ However, this is a difficult test to administer and must be performed under strict medical supervision.²¹

It has been determined that a wheal size of 8.0 mm or greater on the SPT has a 95% to 100% positive predictive value for peanut allergy.^1,26,27 Although conflicting results have been reported in some patients between SPT and the oral food challenge, a negative SPT result is considered useful for excluding IgE-mediated allergic responses.²²

Researchers examining the peanut-specific serum IgE have demonstrated a 95% to 99% positive predictive value when serum levels exceed 15 kU/L.^26,27 This cutoff value in peanut allergy patients is considered suggestive of allergic reactivity, although negative results on an oral food challenge have been reported in more than 25% of children with serum levels exceeding the cutoff.^25-27 Testing may have been to whole peanut extract rather than the molecular components (eg, Ara h8).^11,12

This past summer, the FDA approved a component test that detects allergen components that include Ara h1, h2, h3, h8, and h9.^11,12 Another specific version of the serum IgE test has been in development, one that measures the patient’s IgE reactions to the Ara h2 and Ara h8 components in peanut protein. Johnson and colleagues^10,28 have found an increasing level of serum IgE anti–Ara h2 in children who were unable to pass the oral peanut challenge, whereas serum IgE anti–Ara h8 was higher in those who did pass the challenge.²⁸

DIAGNOSING ANAPHYLAXIS
The manifestation of anaphylaxis in patients allergic to peanuts or tree nuts can be life-threatening.²⁹ Symptoms include intense pruritus with flushing of the skin, urticaria, and angioedema, upper-respiratory obstruction resulting from laryngeal edema, and hypotension.³⁰ The clinical criteria for diagnosing anaphylaxis can be found in Table 2.^30,31

It is important to recognize the signs and symptoms of anaphylaxis in patients with a peanut allergy; many patients who present to the ED represent first-time reactions. Among patients with life-threatening symptoms on initial reaction, 71% will have similarly severe reactions in subsequent episodes (compared with 44% of patients whose first reaction was not life-threatening).³

TREATMENT, INCLUDING PATIENT EDUCATION
Currently there is no cure for peanut allergy, and no appropriate therapies yet exist to reduce allergy severity. Modest gains have been reported in raising tolerance threshold levels through peanut oral immunotherapy—a long, painstaking process.^19,21,32 For now, treatment for peanut allergy is directed at controlling symptoms, once a reaction has occurred. Therefore, the clinician’s goal is to educate peanut-allergic patients and their families on avoiding accidental peanut ingestion, recognizing signs and symptoms of an allergic reaction, and preparing an emergency plan.⁴

Because four in five patients can expect peanut allergy to last for a lifetime,^18,20 strict avoidance of peanuts and peanut products is essential—though difficult because of accidental exposure to food allergens (for example, when dining in restaurants or purchasing bakery products^22,32), cross-contamination (as can occur when a food preparation area is not properly cleaned), and allergen cross-reactivity (such as consumption of other legumes).¹ Patients must be taught to read food labels carefully for possible hidden sources of peanuts (see Table 3^7,8); in some cases, product labels bear helpful advisory wording, such as “may contain peanuts.”^34,35 US legislation mandates that listed ingredients on food packaging include the eight foods that account for 90% of allergic reactions: