What Science Says About Diagnosing Food Allergies

Every food allergy diagnosis should start with a healthcare provider obtaining your clinical history. Be ready to answer a variety of questions about what symptoms you are experiencing, including how often and when the symptoms occur, how long they last, and what you have done to try to alleviate them. Based on your responses, your healthcare provider can decide what testing is recommended.  

Whole allergen specific IgE (sIgE) tests, either in the form of skin-prick testing (SPT) or blood testing, is usually the next step, particularly for those who have hives, vomiting, difficulty breathing, and/or itchy mouth or throat shortly after eating a food or have moderate to severe atopic dermatitis, also known as eczema.¹ An SPT is typically conducted in an allergy specialist’s office, while blood testing can be ordered by any healthcare provider.  

Easier than a midnight dive into Google, right? Keep reading.

Interpreting the results of your sIgE tests can be confusing. Does a positive result mean you are at risk of having a severe allergic reaction? What if you received a positive result to a food you are currently eating without symptoms? How can you be sure you have had all the diagnostic testing you need?

These are all important questions that can arise after whole allergen testing. We know you want to Google. Sit on your hands. Here’s the answer: 

Baseline sIgE tests (both SPT and blood testing) cannot establish how severe a predicted allergy could be; they only show that someone has been sensitized to an allergen. What’s more, these tests can yield positive results to foods a patient is currently eating without symptoms, and allergists are becoming increasingly aware of the dangers of over testing and removing foods from a patient’s diet that the patient is otherwise tolerating.  

The only way to truly diagnose a food allergy is to conduct an oral food challenge. During this test, a patient eats the food he or she may be allergic to slowly and in gradually progressive amounts, while under strict supervision in a medical setting. A double-blind placebo-controlled food challenge is the true gold standard for food allergy diagnosis.² In this type of food challenge, the patient consumes either a placebo or the food allergen separately, usually in two separate appointments.  Since the allergen and the placebo look the same, neither the doctor nor the patient knows what the patient is consuming until after the challenge is completed. Since double-blind placebo-controlled food challenges are time and labor intensive, most often providers opt for open food challenges. In an open food challenge, the patient and the doctor both know that the patient is consuming the allergen.

It’s important to note that oral food challenges are time-consuming, expensive, and potentially risky for patients.² After all, the goal of the test is to confirm whether a patient reacts to a certain food. That means that as the food being tested is ingested in progressive amounts, an allergic reaction is possible—which is why it’s done under supervision and in a doctor’s office. If a meal-sized portion of the food is ingested and there are no symptoms, the patient is discharged after a few hours of observation. On the other hand, if an allergic reaction does occur, the feeding is stopped, and medication is administered as needed. The patient then continues to be observed until the symptoms go away.

Because of the drawbacks associated with oral food challenges, researchers developed a more specific form of sIgE blood testing that can help healthcare providers make a more complete allergy diagnosis and better determine whether someone should avoid a food altogether or go ahead with an oral food challenge.3 This new diagnostic tool, called allergen component testing, can pinpoint the specific proteins that may be causing  food allergy symptoms. That is important because not all symptoms related to the same food are the same, and in fact, two people with an allergy to the same food may be able to manage their allergies differently. 

Ultimately, current research suggests that patients may need a combination of skin-prick testing and sIgE blood testing (both whole allergen and components) to fully understand their food allergies.³ And because allergies can change over time, patients should always follow up with their healthcare providers to see what additional testing, if any, is appropriate for them. 

As the old adage tells us, “Knowledge is power.” Although getting a diagnosis for your food allergy can seem overwhelming at first, it’s important to learn the basics so you are better prepared to work with your healthcare provider to get the care you need and an allergy management plan that’s best for you. For additional tips, check out this resource.