Should I Have Allergy Tests Done (Again)?

Many of us have allergy tests done early in our asthma journey. I'm hitting ten or more years now since my last round of allergy skin tests, and given my two rounds of tests had vastly different results, I've always been curious about if the third time is the charm (or at least would confirm something!) and if it's worth it to have them re-done--especially now that it's been many years!

When should allergy tests be done? Is there a set period of time after which they should be redone, or does it simply follow the regular indications for why someone should have allergy tests? Should I have got the blood test? I'm going to see if I can answer these allergy test questions (and probably more!).

What are allergy tests?

Testing types generally consist of:¹

• Skin-prick tests - a small amount of allergen is pricked/poked under the skin). These are usually used for food and environmental allergies, among others.
• Intradermal tests - a larger (but still small!) amount of allergen is injected under the skin). These tests pose a larger risk of serious reaction than skin-prick tests and are often done if an allergy is suspected but a skin-prick test is negative
• Blood tests - where a blood sample is taken and tested for different allergens, and often a person's IgE level (which can indicate how allergic to stuff they might be). They can also be used in cases where people can't stop taking antihistamines or if they have skin disease that will interfere with testing.

"Challenge tests" can also be done to ensure a person can safely consume small amounts of a past allergen. They are done often after immunotherapy or to check if allergens have been "outgrown." Challenge tests should always be done under medical supervision, especially if there is a history of severe reaction or anaphylaxis.¹

When are allergy tests indicated?

A person should be referred for tests in the following situations:¹

• Persistent asthma
• Suspected allergy to food, medications, insect bites/stings/exposure
• Rhinitis (seasonal, rhinoconjuctivitis, and others)

When should tests be re-done?

The American College of Allergy, Asthma & Immunology (ACAAI) says two years between allergy tests is reasonable.²
Generally, though, there should be an indication for tests to be done (or re-done) such as symptoms (called symptomatic allergy testing) or to monitor response to treatment (called therapeutic allergy testing).²

So basically, yes--if you have new symptoms that indicate the factors covered in question 1--persistent asthma, suspected allergy, or rhinitis--these would indicate it is worth redoing allergy tests.

What's the allergy blood test? Should I have that done?

Allergy blood tests are known as serum tests. The test that used to be done was called the RAST test, but it's not in use anymore. Blood tests are done to check for specific allergens--that said, they are only accurate, per se, if the correct allergen is tested for.¹

IgE is an indicator of allergy, but it is fairly non-specific. High IgE does not necessarily mean a person has more severe allergies--allergies cannot be diagnosed with blood IgE tests alone, so more tests will need to be done if IgE is elevated. Similarly, even those with low IgE can have severe/anaphylactic reactions to allergens. High IgE may indicate chronic allergic disease rather than acute allergies.¹

Allergy blood tests may help your allergist or other doctor make decisions for treating your allergy symptoms--they are just one piece in helping to understand allergies.

What about tests you can get on the internet or at the pharmacy?

While getting allergy tests done by spitting into a tube or submitting hair samples seems attractive, it's simply not accurate. These kits that are available online or at the pharmacy for a couple of hundred dollars test for IgG not IgE. Per allergy dietitian Linda Kirste, IgG tests simply indicate something is present in a person's diet--and that specific IgG can actually go up as the severity of a food reaction goes down!³

I'll cover these tests more in-depth in a future article. Until then, your best bet is to see an allergist, not the internet, for allergy testing.