Nearly everyday I have patients referred to my office from other physicians to help interpret blood tests looking for allergies. All too often, a physician who lacks training in the diagnosis and treatment of allergic disease will order a screening allergy blood test, which measures the amount of IgE, or allegic antibody, in the blood. These screening tests check for a wide range of allergens, including pollens, molds, animal dander, dust mites, and typically a wide variety of foods. While this may sound like a good thing, false positive results are extremely common. For example, particularly in atopic children, it is common for allergy blood tests to show positive results to at least some foods. However, if the child can eat those foods without experiencing symptoms of an allergic reaction, then that child is not allergic to the food in question. The same can be sa id for environmental allergens -- if a person's blood test shows allergic antibodies towards dog dander, but that person experiences no allergic symptoms with dog exposure, then they aren't allergic to dogs. The bottom line is that allergy tests don't diagnose allergies -- taking a good medical history, and using allergy testing as a confirmation, makes the diagnosis of allergies.
Allergy testing measures how a person reacts to specific allergens, such as tree pollen, pet dander, foods, medications or molds. A "positive" allergy test means that a person has a specific allergic antibody to the substance tested. This often means that the person is allergic to the substance, meaning that the person will experience symptoms when exposed to the allergen. However, a positive allergy test does not necessarily mean that the person is indeed allergic to the substance. A person may have a positive allergy test to dog dander, for example, but experience no symptoms with exposure to dogs. In addition, a person may have multiple positive food allergy tests, but be able to eat these foods without any bad reactions.
Symptoms of allergic diseases can certainly give strong hints that a person is indeed suffering from allergies. However, in most cases, various tests are required to confirm a diagnosis. Testing depends on the type of allergic disease in question.
An allergist/immunologist is a medical doctor with specialty training in the diagnosis and treatment of allergic diseases, asthma and diseases of the immune system. To become an allergist, a person must attend college (4 years) and medical school (4 years), and undergo residency training in either internal medicine or pediatrics (3 years each). The physician then must pass a difficult exam to become board-certified in either of these fields. Once board-certified, the internist or pediatrician may decide to obtain additional specialty training in allergy and immunology, called a fellowship (2 years). An allergist/immunologist who is board-certified has also passed an additional examination showing competence in the fields of allergy and immunology.