IgE often plays a central role in the pathophysiology of food allergies, and the classification of food allergies is based on the involvement of IgE in the mechanism of the reaction (ie, IgE mediated, non-IgE mediated, or mixed). Although the skin prick test and the serum-specific IgE test are widely available, any IgE testing should be preceded by a thorough food allergy history to determine the need for specific testing.

Food allergy reactions are either IgE mediated (with symptoms starting within minutes), non-IgE mediated, or mixed. IgE testing should begin with a thorough food allergy history to determine whether the patient’s history and symptoms are consistent with an IgE-mediated mechanism. Testing is not indicated if the history is negative. The patient’s history can provide further insight by defining the type of allergic reaction(s) they experienced in the past, how much food was required to provoke the reaction(s), and the symptoms that were elicited. My current approach to IgE testing includes a thorough history, laboratory parameters, and an oral food challenge (OFC), if necessary.

Most allergists’ offices can perform the skin prick test and might send the patient’s blood for testing. The skin prick test is a functional assay that measures the response of mast cells in the skin to an allergen based on the size of the wheal produced, which indirectly evaluates IgE. The serum-specific IgE blood test measures the free circulating allergen-specific IgE, so it is more quantitative. The 2 tests complement each other because someone can have high circulating serum IgE levels and a very low tissue concentration (or the opposite) and might explain the differences in clinical manifestations. Testing should only be performed by a trained clinician, based on the history and considering the most common food allergens, such as milk, egg, soy, wheat, peanuts, tree nuts, and seafood. Broad test panels that include multiple foods have a high risk of false-positive results and should not be used. The resulting multiple unnecessary dietary restrictions can have a negative impact on the patient’s nutrition and on quality of life for the patient and their family, and they may increase the risk of developing food allergies in the future due to unnecessary avoidance.

The skin prick test is considered positive if the wheal is 3 mm larger than the negative saline control. Probability curves based on the size of the wheal from the skin prick test and the level of food-specific IgE in the blood can help direct our care and can identify the best candidates for an OFC in the clinical setting, which can help determine whether treatment is warranted. Ideally, we would do OFCs to confirm an allergy and establish thresholds (eg, before initiating immunotherapy).

Any clinician who is performing food allergy testing should be ready to do an OFC because of the possibility of false-positive testing and the significant implications of that for patients and their families. Many of the referrals we receive at our allergy center are for patients who had positive allergy tests and are now avoiding the food, and we have to dig deeper to help patients understand whether this is truly necessary. There has to be a very nuanced approach to ordering food allergy testing, and, in my opinion, less is more.