Why perform a food allergy test?

To uncover food allergies to resolve current symptoms or to prevent hidden chronic inflammation from developing into systemic disease. When a person is symptomatic.

Who may be tested for food allergies?

Adults and children over the age of 2 may be tested.

How do you prepare for a food allergy test?

Aim to eat a serving of each of the target foods at least twice in the 7 days prior to testing. 

Is IgG testing for food diagnostic for allergy?

IgG testing for food is not considered diagnostic for allergy because a direct cause-effect relationship has not been firmly established.  In other words, elevated levels of IgG have not yet been proven to cause patient symptoms.  However, more and more studies are emerging to show a correlation between elevated IgG reactions and a variety of conditions.

What are the advantages of blood tests for food allergies?

Although not yet considered the ‘gold standard’ for food allergy testing, blood tests have many advantages over skin prick tests and oral food challenges:

• Condition of skin doesn’t affect ability to test
• Results are reproducible
• No requirement for oral or intradermal challenge, therefore no risk of anaphylaxis from test
• Patient can continue to use antihistamines if necessary

What are the disadvantages of blood tests for food allergies?

• Immunosuppressant drugs may interfere with reactivity and lead to false negative results
• Children under the age of 2 years may not receive accurate results as their immune system is still underdeveloped
• False negative and false positives are possible

What can cause a false positive result?

• Cross-reactivity:  This can occur when the proteins are not identical, but similar enough that the immune system reacts to them.  For example, a reaction to bananas may also produce a reaction to pineapple and vice versa. 
• Leaky Gut:  When the gut lining is inflamed, food particles can leak through and be considered foreign bodies.  This can lead to elevated IgG levels for all the foods the patient normally eats.  Leaky gut may originate with one or more food allergies, or may be a result of stress of prescription drug or alcohol consumption.

What can cause a false negative result?

• No exposure:  If the allergen was not consumed in the 7 days prior to testing for IgG, antibody levels may have dropped enough to decrease reactivity to the food.
• Alteration:  The form of allergen being tested is not the same as what the patient reacts to.  For example, whey protein is altered by high heat, so someone with a whey allergy may have no reaction to heat-altered milk products.  Or, raw eggs show no reaction, but cooked eggs may be a problem.
• Non-Immune:  Other reactions may mimic the symptoms of a food allergy but are not the result of an immune reaction.  For example, lactose intolerance can cause abdominal distress following the consumption of milk products.  Lactose intolerance is due to a lack of the production of lactase, an enzyme that properly digests the milk sugar, lactose.  This is not an allergic reaction, so allergy testing will show up negative (i.e. not allergic to milk) despite obvious symptoms from milk exposure.