Diagnosing Food Allergy: What You Need to Know About False Positive in Skin Prick Test and Blood Work

Disclaimer: I am not an allergist. I have seen a variety of practices among allergists. Some will do wide panel skin prick test (SPT), some will only do SPT when there is a clinical indication for it (ie. hives, other clinical symptoms that points to a suspicious IgE mediated reaction). I believe many are moving towards the later.

In my opinion, there is little value in doing an SPT or bloodwork unless there is a high suspicion of an IgE mediated reaction (eg. hives, swelling, difficulty breathing, etc) due to the high incidence of false positive. It is possible to have positive SPT and bloodwork, and yet be able to eat the food with no difficulty. For example, a patient told me that her baby had a positive SPT for soy and eggs but baby has been eating both with no problem.

A positive SPT in the absence of clinical indication can create unnecessary anxiety and avoidance of a certain food. Ironically, unnecessary avoidance can increase your risk of an IgE mediated reaction in the future. The only way to know if your child is truly allergic to a food is through ingestion. SPT or bloodwork alone should not be used to form a diagnosis, rather it is meant to guide clinical judgment in the context of symptoms. Speak with your allergist if you have questions about your test results.