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.
Allergy Testing: The Skin Prick Test
If you have an allergy, your immune system has a hypersensitivity to a particular substance. This hypersensitivity can be measured through allergy testing. Samples of possible allergens are placed on the skin, which is then pricked gently with needles. If you have a allergy to any of the allergens, the skin will respond with a raised, itchy red bump.
In the case of testing for food allergens, a positive response does not necessarily indicate that the food will cause an allergic reaction when ingested, only that the skin reacts to the food. The test does, however, help determine possible allergens.
Don’t be surprised if the doctor doesn’t do the actual skin pricking: Usually a nurse administers the test and the doctor 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 Testing
If skin testing is not an option for you, your doctor may order a RAST allergy test. The RAST (radioallergosorbant 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, however, 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 don’t have an allergy, but that IgE levels were low at the time of the test. Similarly, high levels of the antibody indicate an existing allergy, but not the identity of the allergen, or even how severe your allergy might be.
Food Allergy Diagnosis
Identifying a food allergy is a little more complicated then diagnosis of an allergy to pollen, dust mites, or the other common airborne allergens.
Your doctor’s first goal is to determine whether you’re experiencing true allergic reactions or some other condition. This is called a differential diagnosis. A true food allergy is relatively rare: Only one to two percent of the adult population has a food allergy. Don’t be surprised if the differential diagnosis determines a non-allergic cause for your symptoms. Possible explanations for allergy-like symptoms include:
- bacterial infection
- food poisoning
- lactose intolerance
- gluten intolerance (Celiac disease)
- reactions to dyes, preservatives and additives
- medical causes, including ulcers and gastrointestinal cancer.
Certain foods, most notably cheese, wine and fish, naturally contain high levels of histamine, which can cause symptoms that mimic allergic reactions when those foods are eaten.
Expect to answer some or all of the following questions during your doctor’s visit:
- Did anyone else exhibit symptoms?
- Do you react to the same substances consistently?
- What other items did you eat with the suspected allergen?
- Was the food prepared and stored properly?
The Elimination Diet
An elimination diet is used to narrow down a list of possible allergy suspects. Under the supervision of a doctor, you eliminate any possible allergens from your diet, substituting nutritionally similar items. You then slowly reintroduce the restricted items to your diet, one at a time, watching for symptoms to reappear. An elimination diet should not be followed if you have extreme allergic reactions such as anaphylaxis: The risk of a dangerous reaction is too great.