Allergies are an immune system reaction to a normally harmless substance. Allergy testing involves having a skin or blood test in order to determine what substance, or allergen, is triggering this allergic response. Usually, allergy testing is conducted through skin tests, which are generally considered more reliable and less expensive than blood tests, though either type of test may be used. By identifying a specific allergen, an allergy sufferer can avoid them as much as possible to reduce the frequency of reactions.
During a skin test, a tiny drop of a solution that contains the possible allergen is placed on the skin, which is then scratched or pricked so that the allergen enters the body. Blood tests screen for antibodies produced in response to allergens. The most common blood test is the enzyme-linked immunosorbent assay, or ELISA, which measures the amount of immunoglobulin E in the blood. Although blood tests can detect a wide range of allergies, including those that may not even produce symptoms, they are less sensitive than other tests.
Reasons for Allergy Testing
Allergies often tend to run in families. If an individual is experiencing typical allergic symptoms, such as sneezing, a runny nose or itchy eyes, testing may be recommended. Although the reasons allergies develop are unknown, there are some substances that are more likely to cause an allergic reaction, including pet dander, bee stings, certain plants or foods and medications including penicillin. Allergy testing is performed to determine if there is a specific substance causing allergic reactions to flare.
Allergy testing may be recommended if the patient has any of the following:
- Nasal congestion
- Swelling or redness on the skin
- Watery or itchy eyes
- Angiodema, a type of swelling that affects deeper layers within the skin, usually around the eyes
- Hay fever, also known as allergic rhinitis, which causes cold-like symptoms including runny nose and congestion
Types of Allergy Testing
There are two main types of allergy testing: skin tests and blood tests. Allergy skin tests expose the patient to small amounts of potential irritants such as pollen, insect venom or animal dander. They are administered in three basic ways: scratch, intradermal or patch tests.
Scratch tests are administered on the forearm, with a drop of each potential allergen applied to a specific spot. Allergy skin tests are used to detect 29 common allergens. Intradermal tests differ from scratch tests since the potential allergen is injected just below the skin, and they are typically only used to test for one particular substance suspected of causing an allergic reaction. Patch tests are conducted with a patch taped to the skin of the upper back for about 48 hours to test for potential reactions.
Allergy blood tests detect and measure the amount of antibodies in the blood that are produced after exposure to an allergen. Whenever a person comes into contact with a substance that may trigger an allergic reaction, the body will produce antibodies against those allergens. The most common form of allergy blood tests is the enzyme-linked immunosorbent assay, or ELISA, which measures the precise amount of the antibody immunoglobulin E in the blood. Unlike allergy skin tests, which provide immediate results, results of an allergy blood test may take several weeks to be processed.
Results of Allergy Testing
Negative results of allergy testing mean that there were no skin changes in response to the allergen, indicating that the patient is not allergic to a specific substance. Although rare, some patients may have a negative allergy test and still be allergic to the substance in question.
When allergy testing yields a positive result, it means that the patient has experienced a reaction to a specific allergen. Usually, the patient develops a red, swollen mark on the arm, known as a wheel. Positive results of allergy testing typically suggest that any symptoms the patient has been experiencing are due to repeated exposure to the allergen. In general, skin tests deliver more accurate results than blood tests.
Considerations of Allergy Testing
Allergy testing is extremely effective for identifying substances that may be causing an allergic reaction. Once allergy testing has identified an allergen, a doctor may recommend certain lifestyle changes to avoid exposure to that specific substance. Patients with allergies may also need to carry medications with them in case they do come into contact with the allergen. While it may not always be possible to prevent an allergic reaction, taking preventative measures may help prevent a serious allergic reaction in the future.