(Allergy) Test Review Session

The two basic types of allergy tests out there- skin prick tests, and blood tests. For the skin prick test, a small scratch is made on the skin, and is then exposed to the allergen in question. If the person is allergic, the scratch will then swell, sort of like a mosquito bite. The main test that our allergist conducts at this point is the blood test, which in our case is the CAP-RAST. Blood is drawn, and the levels of IgE antibodies for various allergens are measured. As I mentioned in the previous post, the IgE antibody level does not indicate "how" allergic the patient is to the allergen- it just indicates how likely it is that the patient is allergic. The "cutoff" level of IgE antibody that determines whether or not you are allergic varies with the allergen. For instance: for eggs, an IgE antibody level of 7 kilo-units per liter (kU/L) indicates a high probability of allergic reaction (95% of patients with this IgE antibody level for eggs will have a reaction). The "cutoff" level for milk, however, is 15 kU/L, and for peanuts is 14 kU/L. This doesn't mean that a patient with an IgE antibody level below these threshholds is not allergic- unfortunately, a reaction can occur pretty much any time the IgE antibody level is higher than zero. On the other hand, a positive test result doesn't guarantee that an allergic reaction will occur either. It just means that the possibility for a reaction is there. So basically, allergy testing can help you determine what foods might cause a reaction (that you therefore should avoid, just in case), but can't determine whether the reaction will actually occur or how severe that reaction could be. (Confused yet? This is why you should always talk to your doctor if you have concerns!)

So on to Bryan's test results. His IgE antibody levels are still extremely elevated for milk, eggs, and peanuts (>100 kU/L for each). They are also slightly elevated for almonds, cashews, hazelnuts, and sesame. Our game plan is to continue avoiding milk, eggs, peanuts, tree nuts, shellfish (as a precaution), and sesame, and re-test in about 12 months. And we'll continue the process until his IgE antibody levels drop low enough that it might appear that he has "outgrown" an allergy or two. At that point, we will look at skin testing, and if those come back negative, it will be time to consider the oral food challenge. But more on that later.