Do you remember high school? I remember the good ol’ days of questionable fashion choices, trying to impress your idiot friends, and the daily battle with teenage acne. I also remember most of my teachers, the classes, and, of course, the tests. While I don’t recall the specific details of each of these tests, I do remember that there seemed to be a considerable difference in the degree of difficulty for each test amongst teachers. For example, some of the teachers wanted to show you how smart they were by inserting an insanely tricky question in the test that almost no one could possibly know the answer to. Other teachers (often football coaches), would make their tests ridiculously simple so as not to risk jeopardizing the starting quarterback’s eligibility on Friday nights. Do we really need a multiple choice question to answer whether or not you have a pulse?
Tests are a tricky thing in both high school and in medicine. Does the coach’s quiz adequately test the student’s understanding of the stuff he covered in class? We should ask the same thing whenever we talk about tests for allergy. Is the allergy test that I am getting actually going to tell me what I am allergic to, or is it just a waste of time and money? A test that doesn’t ask the right questions simply cannot provide you with the correct answers.
In the Karate Kid II, the lead character (Daniel) sees a poster of a man splitting a log in two with his bare hands. He then turns to his sensei and asks Mr. Miyagi if he too was capable of breaking a log like that. Mr. Miyagi simply replies, “Don’t know, never been attacked by tree.” While it may be impressive to shatter logs into toothpicks, the lesson here is that it is not really a true test of whether or not a person can defend themselves in a real fight.
Understanding the way allergies develop is really the key to understanding how to test for them. Your body’s immune system is constantly spitting out a variety of antibodies in an attempt to ward off any would-be intruders. It samples the surroundings (what you eat, breathe, and even touch) to determine what the most likely risks might be. Once you have been infected with a particular bacteria or virus, your immune system usually overcomes the infection and learns from the battle. The next time the bad guys show up, your system will be better prepared to fight them off because it has made antibodies (mostly antibodies termed IgG or IgA) that are specifically designed to defeat the attackers. While these antibodies are great for bacteria, they don’t really serve a purpose for defending us against things that we don’t really need to be protected from like food, grass pollen, or tree pollen (or tree logs).
Because the immune system is so paranoid about the potential for returning invaders, it sometimes gets a little carried away with over-producing antibodies and sometimes makes mistakes and produces a different kind of antibody (termed IgE). In a person with food allergies, these IgE antibodies are formed by the immune system and get stuck onto a particular type of white blood cell called a mast cell. When these mast cells are loaded up with these IgE antibodies on their surface, and then they are exposed to a food allergen that matches up with that antibody, an allergic reaction occurs. That’s when the mast cell spews all of its guts out into the bloodstream, and that’s the reason people get anaphylaxis. This type of allergic reaction can be seriously dangerous and can even result in death.
Because these mast cells don’t have receptors for the other types of antibodies (IgG or IgA), antibodies that are commonly found in the bloodstream against a wide variety of foods won’t cause any type of reaction at all. In fact, almost everyone makes IgG antibodies to foods (assuming they have an immune system capable of generating antibodies). So, if you performed a test to measure IgG antibodies in your blood, what does the result really tell you? The answer is “not much,” and it certainly doesn’t tell you whether or not you are allergic to the food.
In order to determine whether or not an allergy exists, you must look for IgE antibodies. This is done by either an allergy skin test or an allergy blood test. Both ways work, and they are the only ways that experts in allergy and immunology recommend using to determine allergy. Of course, these results need to be interpreted with caution since the most important factor in determining allergy is the patient history.
Some people come into contact with chemicals found in their environment that could cause health issues, and those exposures can be detected using hair analysis techniques, but this is not the type of test that is useful for allergy detection. It only tests exposure, as opposed to antibody development. Tests that measure IgG to foods, hair samples, or any other unproven methods to determine allergic potential are not recommended by any of the major guidelines written by experts in allergy and immunology. While it may seem like we are “splitting hairs” between types of allergy tests to be performed, the type of test you take can make all the difference between an unnecessary test and one that will actually help you defend yourself against any allergic attacks.
References:
1. Middleton’s Allergy Principles and Practice.
2. Choosing Wisely: An initiative of the American Board of Internal Medicine
3. Allergy Diagnostic Testing: An Updated Practice Parameter
4. American Academy of Allergy, Asthma, and Immunology
5. American College of Allergy, Asthma, and Immunology