What Is the Best Method to Diagnose a Food Allergy?

Food allergy testing is tricky, confusing, and far from black-and-white. While we all want concrete answers, allergy testing is much more nuanced and cannot provide clear answers on their own. If you are concerned that you may have a food allergy, your physician will assess your history and will likely conduct food allergy testing to make an accurate assessment and diagnosis.

Physical Examination

Seeing a physician is the first step to determine whether a person has a food allergy. Before diagnosing an allergy, your primary care physician (PCP), allergist, or child’s pediatrician will consider a number of factors before making a formal diagnosis. Your PCP or pediatrician may suggest you connect with an allergist for evaluation and additional testing, if necessary.

First, your physician will take a thorough medical history, including any past allergic reactions. You may be asked the following questions:

• How long after eating the food did these symptoms begin?

• How much of the suspected food did you eat?

• How many times have you had these symptoms?

• Did you take any medication or receive medical care following your symptoms?

  
  

Skin Prick Test (SPT)

This is a very common test that can be done at an allergist’s office to help confirm if a food may be causing symptoms, along with clinical history of allergic symptoms.  Here’s how it works:

• A tiny amount of the suspected allergen substance is placed on the skin (usually on the forearm or back). A single allergen may be tested, or multiple at this time.

• Then the skin is gently pricked with a small probe or needle to scratch the skin, letting the substance penetrate under the surface of the skin. You will be asked to wait to see if a reaction occurs for approximately 15 minutes.
  

If there is a sensitivity, a skin prick test may show redness, or an itchy, raised bump/hive called a “wheal” may appear. The physician/nurse may measure the size of the bump in diameter and take note of this for your chart. Typically, a lack of a wheal or redness indicates an unlikely allergy.

Please remember, however, even if the test is “positive” with a visible reaction, it does not confirm a food allergy by itself. Medical history is the most important indicator a physician will use in diagnosing a food allergy.

Blood Test (Measuring IgE Levels)

This test checks how your immune system reacts to certain foods by assessing IgE antibodies in your blood.

• A small sample of blood is taken and sent to a lab.

• The lab tests it against a list of possible food allergens.

  
  

If your blood responds to the allergen by making high levels of IgE as demonstrated on the results, it might be an allergy. But just like the skin test, this isn’t 100% conclusive on its own. A physician must match the results to medical history for an accurate diagnosis.

Oral Food Challenge (The Most Reliable One)

This is often considered the gold standard for diagnosing food allergies. This should only be done by the guidance of a physician and in a medical setting, unless otherwise advised.

• Very little of the suspected food is given to you at first, then gradually more.

• If you don’t react, you’re likely not allergic to the food.

• If you do react, the team can treat it right away.

Yes, it might sound scary, but it’s controlled and safe. It gives everyone a clear answer on tolerance.

What Is the Best Method for Food Allergy Testing?

There isn’t one single “best” test. The best way to diagnose a food allergy is through a combination of:

• A detailed symptom history

• Skin or blood tests

• And most importantly, an oral food challenge if needed

  
  

The Bottom Line 

If you have a suspected food allergy, please speak with a healthcare provider to obtain an accurate diagnosis. Remember that allergies cannot be diagnosed by one test, alone. An accurate diagnosis should be provided only in the presence of a clinical history, not allergy testing, alone.