What are peanut allergy symptoms and signs? How do physicians diagnose a peanut allergy?
The most important step in the diagnosis of peanut allergy is a detailed history. A good history may essentially make the diagnosis of a peanut allergy. Important factors for a suggestive history of peanut allergy include the following:
Timing of symptoms: The majority of reactions occur within 20 minutes, with nearly all reactions occurring within two hours of exposure to peanuts.
Types of peanut allergy symptoms: About 80% to 90% of reactions involve skin manifestations such as
Nevertheless, reactions can occur in the absence of a rash, and these reactions may be the most severe. Other common signs and symptoms involve the
- respiratory system (difficulty breathing, coughing, wheezing),
- gastrointestinal system (nausea, vomiting, diarrhea),
- cardiovascular system (increased heart rate, decreased blood pressure),
- neurological system (lightheadedness, passing out),
- even changes in behavior, especially in children.
Consistency: Reactions should consistently occur with every peanut exposure.
Following the history, the skin prick test (SPT) is generally the test of choice in making a diagnosis of peanut allergy. It is very important to be aware that a positive SPT alone does not make the diagnosis of peanut allergy. Of note, many individuals with a positive SPT to peanut will not be peanut allergic. The usefulness of a peanut SPT increases as the size of the reaction increases. Sometimes, SPT results are inconclusive and may be followed up with a blood test known as peanut specific IgE levels.
Similar to the SPT, peanut-specific IgE levels must be interpreted based upon the clinical history. Undetectable peanut-specific IgE levels do not rule out the possibility of peanut allergy, with reaction rates of up to 20% being reported in individuals with undetectable peanut-specific IgE. Much like SPT, the likelihood of true peanut allergy increases with increasing levels of peanut-specific IgE.
Despite a thorough clinical history, SPT, and peanut-specific IgE levels, the diagnosis of peanut allergy may still remain in question. In these instances, a physician-supervised oral food challenge (OFC) may be indicated. In an OFC, patients are given gradually increasing amounts of peanut, usually in an allergist's office, and closely monitored for allergic symptoms. OFCs have not only been shown to significantly improve quality of life regardless of whether the challenge is passed or failed, but they have also been shown to be very safe when performed in an appropriate setting under the supervision of a physician experienced in the management of food allergy. During the diagnostic process of peanut allergy, it is also important to determine if peanut-allergic individuals are allergic to tree nuts, since up to one-third of patients with peanut allergy will also react to tree nuts.