Allergic reactions are triggered by the contact, inhalation, or ingestion of a number of different allergens. Some of the most common allergens are made up of proteins found in plants, mold, food, venom, animal skin, and medication. Symptoms of allergic reactions range from mild irritation such as itching, wheezing, and coughing to life-threatening conditions related to the respiratory and gastrointestinal organs. Serious allergic reactions are more likely to result from food, drugs, and stinging insects. A person does not become allergic to a particular substance until after the first exposure. However, in some cases, even trace amounts of a substance, such as peanuts or seafood in a mother’s breast milk, can cause an allergic reaction in a subsequent exposure.
A variety of allergy tests are available for determining specific substances that trigger allergic reactions in individuals. Allergists, also known as immunologists, are trained in selecting the types of tests that are both safe and appropriate, depending on the suspected allergies. By using allergen extracts, tiny amounts of commonly bothersome allergens (usually in the form of purified liquid drops), immunologists are often able to isolate which substances cause reactions in allergy sufferers.
One of the most common types of environmental allergy tests is the skin- prick test. This technique involves placing small drops of potential allergen onto the skin of the forearm about one to two inches apart. After the drops are placed on the arm, a needle is used to puncture the skin at the site of each drop. (Though the procedure is virtually painless, this test is often done on the upper back of children to prevent them from seeing the needle.) If an allergy is present, an allergic antibody called immunoglobulin E (IgE) will activate a special cell called a mast cell. Mast cells release chemicals (also known as mediators) that cause itching and swelling. The most common mediator is histamine. Histamine is what causes the controlled hive known as a wheal and flare. The white wheal is the small raised surface, while the flare is the redness that spreads out from it. In an uncontrolled allergic reaction, wheals and flares can get much bigger and spread all over a person’s body. Results from a skin test can usually be obtained within 20 to 30 minutes, while the reaction usually fades within a few hours.
Another test that is very similar to the skin-prick test is the intradermal allergy test. This involves placing the allergen sample under the skin with a syringe. The intradermal test involves more risk and is usually saved for use if the allergy persists even after a skin-prick test comes back negative. People who have experienced serious allergic reactions called anaphylactic reactions are not advised to have these types of tests. These allergy sufferers may be hypersensitive to even trace amounts of the allergens when they are introduced into the blood. Anaphylaxis is an allergic reaction that affects the whole body and is potentially life-threatening. Hives on the lips and throat can become severe enough to block air passage. Anaphylactic shock occurs when enough histamine is released to cause the blood vessels to dilate and release fluid into the tissues. This lowers blood volume and can result in heart failure.
A blood test can be performed to safely isolate over 400 different allergies, including dangerous food and environmental allergens. The Radio Allergo Sorbant Test (RAST) measures specific IgE antibodies using a blood sample. IgE is normally found in very small amounts in the blood; it is created as a defense mechanism when it senses an intruder. Separate tests are done for each potential allergen, and IgE results are graded from 0 to 6. For example, canine serum IgE will be high if a person has an allergy to dogs. The RAST is used if patients have pre-existing skin conditions or if patients cannot stop taking certain medications such as antidepressants or antihistamines for even a short period of time. (People must stop taking antihistamines several days prior to taking a skin allergy test because the medication can interfere with the results.) The RAST is a more expensive test that does not provide immediate results.
A number of other allergy tests are available, though many are considered unreliable according to The Academy of Allergy, Asthma, and Immunology. Applied kinesiology is a test that analyzes the loss of muscle strength in the presence of potential allergens. Provocation and neutralization testing involves injecting food allergens into the skin in different quantities, with the goal of determining the smallest dose needed to neutralize the symptoms. Sublingual provocation and neutralization is a similar test, except that the allergens are injected underneath the tongue. Cytotoxity testing involves watching for the reaction of blood cells after placing allergens on a slide next to a person’s blood samples.
After using a reliable testing method, the cause of an allergic reaction is often identified, and a physician is able to help a patient develop a treatment plan with the goal of controlling or eliminating the allergic symptoms. Those who are allergic to furry pets, pollen, and plants are prescribed mild medication or taught how to control their reactions with simple lifestyle changes, while those with food allergies learn to safely remove certain foods from their diets. Allergy sufferers who are prone to anaphylactic reactions are educated about life-saving techniques such as carrying the drug epinephrine and wearing medical alert bracelets. As soon as people understand their allergies, they can begin to experience an improved quality of life.
The passage describes three different types of allergy tests. Which of the characteristics below belongs to which type of test? In boxes 1-7 on your Answer Sheet, write
A if it is a characteristic of the skin-prick test.
B if it is a characteristic of the intradermal test.
C if it is a characteristic of the blood test.
1 A substance is inserted beneath the skin with a needle.
2 It is often done on a patient’s back.
3 It is advisable for patients who have skin problems.
4 It is not advisable for patients who have had serious allergic reactions in the past.
5 It shows results within half an hour.
6 It can cause red and white bumps on the patient’s skin.
7 It has a higher cost than other tests.
Complete the summary of the reading passage below. Choose your answers from the box below, and write them in boxes 8-14 on your Answer Sheet. There are more words than spaces so you will not use them all.
Allergic reactions result from touching, breathing, or (8)……………………..certain substances called (9) ………………… Coughing or itching are two possible (10)………………….of an allergic reaction. More serious allergic reactions may result from certain insect bites, foods, or (11)………………………..A severe allergic reaction is known as (12)……………………….It can result in loss of blood volume and heart failure. Doctors can use a variety of tests to (13)……………………the source of an allergy. Treatment may include taking medication or (14)…………………………the substances that cause the allergic reaction.