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The Biggest Allergy Skin Testing Mistake: Re-Skin Testing

The Biggest Allergy Skin Testing Mistake: Re-Skin Testing

By: Dean C. Mitchell, MD, Board Certified Immunologist and author Allergy & Asthma Solutions

Allergy prick skin testing is considered the gold-standard for diagnosing immediate allergy to environmental and food allergies.

MRS Allergy is carefully training doctors all over the United States how to perform prick skin testing properly. In the past, allergy skin testing was mainly done by allergists and ENTs, but this has changed in recent years.  Today, pediatricians, family physicians, related specialties (ophthalmology and dermatology) and even Urgent Care physicians are using this testing to specifically diagnose their patient’s allergic symptoms.

IgE vs. IgG

Allergy prick skin testing measures the allergen’s reaction to IgE on the patient’s skin cells. IgE is associated with immediate allergic reactions that are associated with airborne allergens such as: dust mites, animal dander, pollen and molds. It also involves the dangerous reactions regarding foods such as peanuts and shellfish. The allergy skin tests once applied will set off a histamine type reaction within 15 minutes that can be easily measured for the size of the induration(swelling- not the redness).

Patients that show a positive reaction to an allergy skin test reflect an IgE reaction, and if their clinical history matches up are diagnosed with clinical allergy. In the past, patients had a choice of taking daily antihistamines or receiving allergy injections to reduce their symptoms. Today, through MRS, patients also have a choice of using sublingual allergy drops to reduce and reverse their allergies. It’s important to note that antihistamines or topical nasal cortisone sprays(e.g. Flonase) don’t block the IgE response from the patient- and as a result do not give long-lasting protection. Allergen immunotherapy, whether by injections or sublingual drops can achieve immune protection that is lasting. How does that work?

Allergy immunotherapy is also referred to as desensitization- meaning the patient is given the actual allergen they are allergic to initially in small doses and that over a period of months is treated with stronger concentrations of the allergen. This is done until a patient reaches a maintenance dose of the allergen which provides immune protection.

The immunological mechanism by which this occurs is by the patient building up specific IgG antibodies to the allergen- which has been called the “blocking antibody” because scientific research supports this IgG antibody as the reason a patient doesn’t experience the allergic reaction anymore.

What happens to IgE during this time? Does it go down or disappear? Actually, no. The specific IgE that was recorded on the patient’s skin test doesn’t change very much, but it is blocked from causing an allergy by the increase in specific IgG. This is the reason why you should not re-skin test the patient. The allergy skin test done on a patient a year, or two or three years later will not change very much(because remember the IgE doesn’t decrease) even after allergy injections or drops; however, what we do see is that the patient is clinically better. How do we know that? They tell us of course, but for documentation purposes, it is highly recommended that your patients fill out the comprehensive Allergy Questionnaire at the beginning of treatment and then have them fill it out on an annual basis.

Below is a diagram showing the mechanism how allergen immunotherapy affects the key immune cells. This was shown in my book Dr. Dean Mitchell’s Allergy and Asthma Solution (DeCapo 2006) and reprinted from The Journal of Allergy and Clinical Immunology.

Conclusion: Remember, don’t make the mistake of performing Allergy re-skin testing on a patient you are following on allergen immunotherapy- it won’t change, or improve as you might suspect. Instead, use your Allergy Questionnaires and try to simply explain to the patient if they are clinically better they have developed blocking antibodies.