Elyra D. Figueroa, MD
Allergy, Asthma & Immunology
Institute of St. Louis, Inc.
Skin + Laser Institute of St. Louis
What is Allergy Testing?
Skin prick Testing
Skin prick testing is the most common method of allergy testing for environmenal and food allergens. With this test, the skin is slightly pricked while a small drop of allergen is exposed to the skin for about 15-20 minutes. Dr. Figueroa will then monitor the skin for signs of an allergic reaction, including redness and swelling. You can expect to experience some discomfort when your skin is being pricked, and also some itchiness while the allergens are allowed to react.
Intradermal testing is similar to skin prick testing for environmental allergens only, the major difference being that the allergen is injected under the skin to form a small bubble. If you are familiar with the test used for tuberculosis, it is the same type of injection. Intradermal testing can be more sensitive than skin prick testing. Intradermal testing is also used for testing for an insect sting allergy.
Patch testing may be used when you have been experiencing allergic reactions on your skin. For example, if you develop a rash after using a new shampoo or wearing a new piece of jewelry. During the patch test, a substance is placed on a patch that is then applied to your skin. After about two days, the patch will be removed to see if you have any allergic reactions. Dr. Figueroa will want you to return later in the week to check for any delayed reactions.
Blood testing may be recommended to measure the antibodies for environmental or food antibodies present in your blood but it is not as accurate as skin testing. One common blood test in the field of allergy measures Immunoglobulin E (IgE). IgE is an antibody that your immune system develops in reaction to a specific allergen. Other relevant blood tests include radioallergosorbent testing (RAST), eosiniphil counts, or immunoassay capture test (ImmunoCAP).
How do I know if I have allergies or a cold?
The symptoms of allergies and cold can be similar and difficult to distinguish. However, certain characteristics may be helpful in distinguishing the two. For example, presence of a fever usually indicates a cold and not allergies. On the other hand, if you get symptoms after exposure to specific environmental trigger, like exposure to cats, dogs, dust, this generally indicates the presence of allergies. Dr. Figueroa will be able to confirm the diagnosis of allergy by taking a detailed medical history and appropriate allergy testing.
I’ve never had allergies before, why do I have them now?
The reason for this might lie in the root cause of allergies. It is thought that they occur due to a combination of genetic (inherited) susceptibility to allergies and specific environmental conditions that the person is exposed to. In most people allergies develop in childhood and may persist through adult life. However, it is not uncommon to develop allergies for the first time in later life. Such people might not have had the specific environmental exposures until later in life. For example, some people develop allergies after moving to a new city or country where they are exposed to new allergens in the air like pollens or animal dander. It takes months to years to develop sensitization to new allergens after moving to a new place and develop symptoms. Often, allergy symptoms began soon after arriving to the new location. This could likely be due to a preexisting allergic sensitivity, but a much higher level of exposure to the potential allergen trigger in the new environment.
What are antihistamines?
Anti-histamines are commonly used over-the-counter and prescribed medications that are used in the treatment of allergies. Many of the symptoms of allergies are due to a chemical produced in the body known as histamine. Histamine binds to histamine receptors in various tissues in the body resulting in a multitude of allergy symptoms such as a runny nose, itchy eyes and hives. Anti-histamines block these receptors and prevent histamine from binding thus helping to reduce the allergy symptoms experienced. Antihistamines do not prevent alleriges or treat the subsequent inflammation from the expsoure to the allergies.
How do I know I’m allergic to a specific food?
Most allergic reactions to foods occur within minutes of consuming the particular food. Symptoms may consist of the following:
Hives or red/itchy skin
Stomach pain, nausea, vomiting or diarrhea
Itchy/runny nose, sneezing or itchy/watery eyes
In some cases the allergic reaction may be severe and life threatening. Such a reaction is called anaphylaxis and may consist of:
Swelling of face/lips/throat, hoarseness, lump in throat
Cough, difficulty breathing, wheezing or chest tightness
Feeling faint or dizzy, palpitations, tingling and numbness in fingers
Feeling of impending doom
Call 911 immediately if you experience any of these severe symptoms.
Dr. Figueroa will be able to confirm the diagnosis of food allergy using a detailed clinical history, skin testing and blood tests.