Allergen skin testing provides important information about how allergy cells in the area respond when exposed to an allergen
Given the complexities of the immune system, “challenge” tests – which are tests that directly engage allergy cells with allergen to evaluate what happens – are currently the most diagnostic allergy tests clinically available. The most common allergen challenge test performed clinically is allergen skin testing, in which allergen is introduced into the skin to interact with the allergy cells present there. Activation of those allergy cells typically results in a localized hive at the site of the skin test.
When allergen is present in large enough amounts near an allergy cell that is primed with enough specific IgE for that allergen (meaning enough specific IgE antibody for that allergen is already bound to the allergy cell), the allergen binds to multiple of its IgE antibodies (called cross-linking), and activation of that allergy cell can occur. Activation of allergy cells causes the symptoms of allergic reactions.
If activation of your allergy cells is likely to happen due to a particular allergen, you are diagnosed with an allergy to that allergen. Allergen skin testing provides a low-risk glimpse of this potential.
There are two main types of allergen skin testing used to help in the evaluation of potential allergies – skin prick testing (SPT) and intradermal testing (IDT)
Skin prick testing is minimally invasive and involves pricking the outer surface of the skin with either a commercial allergen extract or the fresh allergen if needed. Intradermal testing is slightly more invasive and involves a small injection of a solution containing allergen that is placed just underneath the surface of the skin.
These skin tests are done on areas of the body that generally contain a substantial number of allergy cells, such as the arm or the back, and they are read for results during your appointment about 15-20 minutes after being placed. At Allergenuity Health, we attempt to be as least invasive as possible while getting the information we need to best help you with your goals.
At Allergenuity Health, we choose what to skin test you (or your child) to based on your specific situation and the information needed (we do not use large, generalized panels)
Since allergen skin testing is not a perfect diagnostic test, we do not believe that the best typical approach to diagnosing allergies is placing numerous tests on your skin from a large, generalized panel. Instead, Dr. Schroeder will choose which specific allergens or groups of allergens you (or your child) should be tested for based on factors related to your own specific history, allergic conditions, and goals. This allows us to get the important information we need to best help you, while minimizing the invasiveness of the testing, your physical pain and side effects from the testing procedure, and the confusion that often follows when a patient is given the “results” of these large generalized panels.
Allergen skin tests are generally low risk and without significant side effects, but rarely a more severe reaction can occur so it is important to be tested in an appropriate medical setting
Most often, allergen skin tests result only in mild localized itching and swollen bumps (like a hive or mosquito bite) where tests are positive. These symptoms go away on their own within the day, and sometimes an ice pack, a topical steroid, or an antihistamine may be helpful. Less often, a delayed reaction can occur at one or more of the test sites after you have left the office, resulting in an area of swelling, tenderness, redness, and possibly itching that can last for several days. Rarely, introduction of allergens into the skin can produce a severe immediate allergic reaction that requires treatment immediately, which is why it is important to have your skin tests performed in the office.
Your skin’s reactivity can change due to many factors, so 2 scientific control tests are also done to help with proper result interpretation
In addition to the allergens being tested, we will place two scientific control tests on the skin as well. The positive control test is typically conducted with histamine and demonstrates whether or not the skin is responsive to histamine at the time of testing. Medicines like antihistamines, some heartburn medications, several antidepressants, and others can interfere with skin test results and should be stopped several days prior to your appointment as long as stopping them will not significantly affect your health (this should be discussed with your doctor). Natural chemicals found in many foods, beverages, and supplements can also suppress your skin’s response to histamine release. Since histamine is one of the major chemicals released by activated allergy cells, if the skin is not responsive to the histamine in the positive control test, allergen skin tests done that day that otherwise would have been positive could appear negative. This would provide misleading information if interpreted without this context.
The negative control test demonstrates whether or not the skin is reactive to pokes, pressure, or the other components in the allergen solution. If the skin is reactive in this way, allergen skin tests that otherwise would have been negative could appear positive, which would provide misleading information if interpreted without this knowledge.
A “positive” skin test result does not necessarily indicate that you are allergic, and a “negative” skin test result does not necessarily indicate that you are not allergic. Skin tests require interpretation within a much larger context to have meaning
Our approach to skin test result interpretation is integrative, personalized, and thorough in order to give you an accurate picture of your current health status, your diagnosis, and the most appropriate treatment options for you. Allergen skin testing has many strengths but also has many limitations, and these all need to be taken into account along with your medical history, allergic conditions, and environmental factors in order to best determine what an allergen skin test result may mean for you.
Allergy cells throughout different areas of the body can have different characteristics and therefore may react differently when stimulated by a particular allergen. This means that it is important to keep in mind that the result of a skin test in one localized area provides important information but may not tell the whole story about how allergy cells in your nose, eyes, airways, gastrointestinal tract, other areas of the skin, or brain may respond when stimulated by that allergen.
Commercially prepared antigens have been modified from their raw form due to the purification process (which allows them to be safely used for testing and treatment), and antigens from different companies or even different batches from the same company are not all equitable. So a commercial antigen for “dog allergen” will likely contain many of the important dog allergens but may be missing some major or minor ones that are also important for some people, and one company’s dog allergen extract may be quite different from another company’s, yielding different skin test results.
Allergy cells in the skin persist for a long time. This means that skin tests results often do not change as early or as dramatically as some other areas of the immune system when a person is on an immunotherapy treatment, so notable symptom relief is often present before significant changes in skin tests. Because of this property, skin tests don’t need to be repeated very frequently, but following skin test results over appropriate time intervals can be very helpful in assessing possible immune system changes or status on treatment.
Proper interpretation of allergen skin test results by someone knowledgeable in all these factors such as an allergist is critical to most accurately diagnosing and best treating allergic disease
At Allergenuity Health, a board-certified allergist will work together directly with you to ensure that you feel comfortable understanding what your skin tests do and do not mean with regard to both your allergic conditions and your status on sublingual immunotherapy treatment.
As the performance of allergen skin testing becomes more broadly available by companies and different types of providers, it is important to remember that your allergy skin test results are not 100% diagnostic of allergy but rather are just one piece of a larger story. These skin test results require interpretation within a much bigger context to have meaning regarding an allergy diagnosis or status on a treatment. When allergen skin tests are used by some as a simple “positive” or “negative” and therefore “yes” or “no” in terms of an allergy diagnosis, your results may seem confusing and your treatment may unfortunately lead you down a path that is not necessarily the best course for you – potentially restricting foods you do not need to, taking medications you don’t need, or conversely eating something that could be dangerous for you, or being told you are not allergic when in fact you are. Any time your skin tests are done with us, we will not only provide you with your results but also our interpretation of what they mean for you specifically.