Allergy Testing and Diagnosis
Determining whether you have allergies, and then finding out what the allergen is, can take time and patience. Some allergy symptoms have obvious causes: if you break out in hives every time you eat shellfish, chances are good there’s a connection. Other allergy symptoms don’t stem from an obvious source: if you suffer from hay fever, is it because of tree pollen, dust mites, or the family dog? Allergy testing may be necessary to identify the offender.
The first step is to talk to your doctor or health professional about your allergy symptoms. Expect to answer a number of questions. Your doctor may ask whether you have a family history of allergies, when the symptoms occur, and what you were doing at the time the symptoms appeared. The doctor may also want to know where you were when you reacted, if you’re taking any medications, or if you have a medical condition that might mimic an allergic reaction. Depending on the results of the exam, you may be referred to an allergist for testing.
Skin Pricking: Taking an Allergy Test
If you have an allergy, your immune system has a hypersensitivity to a particular substance. This hypersensitivity can be measured by taking an allergy test. Samples of possible allergens are placed the skin, which is then pricked gently with needles. If you are allergic to an allergen, the skin will respond with a raised, itchy red bump.
Don’t be surprised if the allergist doesn’t do the actual skin pricking: usually a nurse administers the test and the allergist examines the results. The skin pricking can be uncomfortable, but is not usually reported as painful by patients.
Certain medications can interfere with the results of an allergy test. Antihistamines and antidepressants, for example, and some types of heartburn medications and sleeping aids can interfere with the accuracy of test results.
Some allergens can’t be tested by skin pricking, and people with extreme hypersensitivity should not undergo skin testing because of the risk of anaphylaxis. Severe dermatitis or eczema can also make skin testing intolerable.
RAST Allergy Test
If skin testing is not an option for you, your doctor or allergist may order a RAST allergy test. The RAST (radioallergosorbent test) is a blood test that measures the levels of IgE antibodies in the bloodstream. IgE antibodies are produced in response to the presence of allergens, so a positive result indicates that you’re probably allergic to something. The test doesn’t tell you what you’re allergic to—only that you probably have an allergy.
Note that a RAST allergy test is only a guideline. A negative result does not mean that you have no allergies, but that IgE levels were low at the time of the test. Similarly, high levels of the antibody indicate allergies, but not the identity of the allergen, or even how severe your allergy symptoms might be.
The Elimination Diet
An elimination diet is a useful method for pinpointing food allergens. Suspected allergens are removed from the diet for several weeks, and then slowly added back into the diet one at a time. Presumably, with all suspects removed from your diet, you are free of allergic symptoms. As the allergen is reintroduced, you should be able to identify it because you have an allergic reaction to it.
Given the nature of an elimination diet, people who have severe allergic reactions should not use it to narrow down allergens. The diet essentially invites an allergic reaction (which confirms the allergen). Those who suffer from life-threatening allergic reactions would put themselves in danger if they used an elimination diet to determine the cause of their allergies. Consult your doctor before starting such an experiment.