By Sharon Stewart Blake, Tests.com Contributing Writer
Allergy testing—usually in the form of a skin test or a blood test—is performed in a doctor’s office and helps determine what particular substance or allergen prompts an allergic reaction in a person. Those who suspect allergies to pollen, mold, cats, dust, milk, eggs or wheat can test at home before visiting the doctor using a kit.
Once a specific allergen is identified, a doctor can develop a treatment plan aimed at controlling the symptoms. The American Public Health Association says more than 50 percent of the US population ages 6-59 have had a positive skin test to at least one allergen.
How Allergy Tests Work
People with allergies have an allergic antibody or chemical in their blood called immunoglobulin or IgE. When someone is exposed to a potential allergen the first time, they become sensitized, and their body produces IgE. It activates special cells called mast cells, found throughout the body but in highest concentration near the skin. The next time the body is exposed to the allergen, the IgE antibodies recognize it and produce mast cells which, in turn, release chemicals called mediators. Histamine, for example, is a mediator that causes redness and swelling. In testing, this swelling appears only in the spot where the allergen has been introduced.
Types of Allergy Tests
There are two common ways to test: through the skin and the blood. Skin tests are used
more frequently because they are fast, reliable and less expensive than
Skin Prick Test
This is the most common allergy skin test. A series of needle pricks is created on the skin and then tiny droplets of various purified allergen extracts are inserted. If an area develops an itchy red bump called a “wheal” within about 20 minutes, the test is positive. This usually means the person is allergic to that substance. Skin pricks are frequently used in food allergy testing and to determine allergies to pet dander, dust mites, pollen, mold, penicillin and insect venom.
More sensitive than the skin prick test, this test involves the doctor injecting purified allergen extracts just under the skin of the arm. This is done if the doctor already suspects the person is allergic to penicillin or insect venom or if the skin prick tests are negative.
The doctor applies the allergen to a patch and tapes the patch to the skin for 24 to 72 hours. This is done to identify allergens that cause a skin allergy called contact dermatitis. These allergens may include fragrances, medications, preservatives, metals, hair dyes and latex. Since the use of latex gloves for many procedures has increased dramatically in recent years, the Pennsylvania Health Department estimates 8% to 17% of health care workers routinely exposed to latex gloves have developed a sensitivity to the proteins and chemicals in latex.
An allergy blood test is called a radioallergosorbent tests or a RAST allergy test. In this test, a person’s blood is drawn and checked for an allergic antibody called immunoglobulin E or IgE. People with allergies have this antibody; it functions as part of the body’s immune system. While blood tests are more expensive and not as sensitive as skin tests, they are used on people who are unable to have a skin test, such as those who have a skin disease, who are highly sensitive to suspected allergens or who are on a medication that could interfere with the test results, such as antihistamines, antidepressants or heartburn medicine.
Home allergy test kits use a small blood sample for the allergy test. Testers will use a device to prick their finger and collect the sample, which is mailed to a lab. Once there, the testing is the same as if the sample were collected in the doctor’s office.
Who Should Get an Allergy Test
If a person suffers symptoms like watery eyes, hives or dermatitis year-round or at a particular time of year or during an exposure to a particular substance, an allergy test could be helpful in pinpointing a possible allergen. Children under six are especially vulnerable to food allergies. Both adults and children over the age of three may get allergy tests. While the skin prick test is done on an adult’s forearm, children receive the test on their upper back.
Before an allergy test, a doctor will require a detailed medical history. Patients must be prepared to answer questions about family history, current medication, illnesses, emotional and social conditions, eating habits and lifestyle. The doctor will check one’s ears, nose, throat and skin during a physical examination.
Patients should not take antihistamines before a skin allergy test, as it may cause a false-negative result. Both the skin prick test and blood test take less than an hour. Skin test results show in about 20 minutes. It may take days to get blood test results because the blood is sent to a lab.
In rare cases, skin testing can cause an anaphylactic reaction, which can be severe and potentially fatal. Emergency equipment should be readily available wherever allergy testing is performed.
Most health insurance plans cover the cost of an allergy test in a doctor’s office. In-home allergy test kits are offered in stores or online for about $50.
Are you considering an allergy test? Please see our Allergy Test Directory for more.