Q:

5/22/2014
I have a 52 yo female blood tested positive for dozens of food & environmental allergies from avocado, rye, wheat, to celery, paprika & garlic. OK lamb & pork. Total IgE 921. She had a titanium rod placed 2009 for C5-7 fusion and later tested positive for titanium oxide allergy. Is there some likelihood of false positives in some of the food allergens given so much inflammation? Or are tests in Class 3/High range pretty reliable + results no matter what?

A:

Thank you for your inquiry.

Any positive tests to detect an allergen that may cause an immediate hypersensitivity reaction (allergic asthma, allergic rhinitis, or anaphylaxis for example) detects only the presence of specific IgE directed to the allergen in question. The presence of specific IgE increases the statistical likelihood that exposure to the substance will produce an allergic reaction. However, one can be sensitized to the substance - that is, have specific IgE directed to it - but not have a reaction when exposed. This state is called sensitization without clinical reactivity. In regards to food allergy testing, the specificity rate - that is, the presence of a reaction to a food in a patient testing positive - can be as low as 60%.

The sensitivity and specificity of the test varies considerably depending on the food tested and the exact nature of the in vitro test employed. The level of sensitivity, does predict the frequency of reactivity; that is, a patient with a "4+" reaction would be more likely to react to a food in general than a patient with a "1+" reaction. However, clearly, patients can have 4+ reactions and still not react to the food.

So, in direct answer to your question, "false-positives" in the case of in vitro tests for food allergy are not uncommon. And although the statistical likelihood of a reaction is higher with a Class 3 or 4 than with a Class 1 reaction, there are many instances of Class 3 and higher reactions occurring in patients who can ingest a food without difficulty.

In reality, the only definitive test for allergy to food is an oral challenge.

Applying these principles to your patient, it is not unlikely that many of the tests could be, "false-positives." That is, I would not be surprised if your patient could eat many of these foods without difficulty, even when the class is 3 or above. The tests themselves, therefore, have to be interpreted in light of the history, and routine withdrawal of foods which have been ingested without difficulty is not indicated regardless of test results.

There is an excellent article which is available to you free of charge here that deals with in vitro testing to foods.

Allergy blood testing: A practical guide for clinicians
ROXANA I. SILES, MD and Fred Hsieh, MD
Cleveland Clinic Journal of Medicine, September 2011 vol. 78 9 585-592.
False-positive and false-negative tests are common in any form of allergen testing. Tests to titanium usually are done to detect delayed hypersensitivity to that metal, most often due to contact with the metal via the skin or through an implant. In general, these tests have been validated to a lesser extent than tests for immediate hypersensitivity to foods, and the interpretation of results is less well developed at this point in time. False-positives as well as false-negatives can occur. To comment further about the test to titanium we would need more information as to why the test was done, the clinical manifestation of metal allergy and the specific test performed. But we have several entries on our site dealing with metal allergy and you can access them by using our search box. A few deal specifically with titanium.

Thank you again for your inquiry and we hope this response is helpful to you.

Sincerely,
Phil Lieberman, M.D.

AAAAI - American Academy of Allergy Asthma & Immunology