Allergy tests: What to know

Results from some medical tests are easy to interpret. If your throat is swabbed for a streptococcal infection and it comes back positive, you know you have strep throat. At-home pregnancy tests are 99% accurate. Patients with Type 1 diabetes track their own blood glucose and monitor the results.

So you might think it would be just as easy when looking at the results of your allergy tests. Sometimes it is and sometimes it isn’t. There are many different “allergy” tests that can be done at home or in a physician’s office, and because not all tests — especially home tests — are Food and Drug Administration-approved or reliable, this may lead to difficultly in understanding the results.

[Read: Is It COVID-19, Allergies, Flu or a Cold?]

Types of Allergy Tests

According to the American College of Allergy, Asthma and Immunology, when testing for true allergy to foods, indoor and outdoor allergens (such as cats and pollen), certain medications and stinging insects, there are two main types of tests:

— Allergy skin tests.

— Allergy blood tests.

By “true allergy” we mean you have an antibody (called IgE) to a substance. An antibody is a protein that’s made by a type of white blood cell. It’s made in response to an antigen, like a food or dust or a drug or a pet. The antibody binds to mast cells, and when you’re re-exposed to the antigen, it can bind to the Ig antibody on the mast cell. The mast cell explodes and releases chemicals like histamine and other chemicals that lead to symptoms ranging from sneezing, wheezing and hives to severe life-threatening anaphylaxis.

Skin tests are performed by taking different substances you may have an allergy to and pricking the skin with them, according to the American College of Allergy, Asthma and Immunology. If this causes a small hive and redness appears after a few minutes, it means that IgE to that substance is present.

For allergy blood tests, the IgE level to different substances is measured. You then get a report back showing whether there is IgE antibody, and if it’s present, the level detected in the blood.

[See: 9 Most Common Food Allergies.]

Reading Allergy Test Results

Say you got hives soon after eating a peanut, and the allergy skin test was positive to peanut; this would confirm that you have peanut allergy. That is straightforward. Here is where confusion can occur: Just because you have a positive allergy skin or blood test, it doesn’t mean you are always “allergic.”

For example, let’s say you see an allergist because you experience sneezing and nasal itching only during the spring. You have allergy tests done and it’s positive for oak tree and ragweed. We know that oak tree pollinates in the spring, and ragweed pollinates in the fall. Therefore, you show what is called “sensitivity” to ragweed, but it’s not currently causing clinical problems for you because you are well into fall. In other words, a positive skin test does not prove true allergy because it needs to correlate with your clinical history. In this example, there is no reason to treat the ragweed allergy because it’s not causing any health problems.

Here is another common occurrence. You think you might have food allergies as you have developed some hives off and on, but you can’t pinpoint what caused them. Your physician orders a food allergy blood test that checks for IgE antibodies to 25 foods. The results show a low level of IgE antibody to milk. Does this mean dairy products caused the hives and you can never consume them again? No — all the test indicates is that you are “sensitized,” but it does not mean it’s causing the hives and you are allergic to milk.

Confirming Your Allergies

An oral challenge (during which you actually consume milk) should be done in an allergist’s office to see if it reproduces the hives. If it doesn’t, then you can go back to enjoying dairy products.

Remember, a positive allergy skin or blood test to foods does not mean you are truly allergic to them. Your medical history on exposure to the food and a possible challenge to the food are the only definitive way to say you have a true food allergy.

[READ: Food Allergy vs. Food Sensitivity: What’s the Difference?]

Food Allergies vs. Food Sensitivities

It’s possible you’ve heard of IgG antibody tests for food reactions done on a blood sample. IgG tests have become popular in recent years. What is the difference between an IgG antibody test and an IgE antibody test?

IgG is the major protein in the body that fights infection. It leads to long-lasting immunity after you get a vaccine. It’s not uncommon for the body to make IgG antibodies to food, but IgG does not cause a true allergy in the way that IgE does. The manufacturers of IgG tests say they help diagnose sensitivities or intolerances to foods causing reactions such as headaches, gastrointestinal problems, joint pain and general fatigue.

Presently there is no scientific evidence that these tests are accurate. They are not approved by the FDA and not covered by insurance like IgE-based allergy tests are. The only way to determine if a particular food is causing a “sensitivity” is to eliminate it from your diet for several weeks and see if the problem resolves. If it does, reintroduce the food and see if symptoms redevelop. If that happens, the food is probably the cause.

If you think you have allergies of any kind and want to determine the cause, evaluation by a board-certified allergist trained in proper testing can get you the answers you need.

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