How Do I Interpret Allergy Test Results?

Recently a reader posted this question here at HealthCentral.com, saying that her child had results like this: Trees 2++; Grass 4++++. She wanted to know what the numbers mean.

First, let me say that interpreting allergy test results is a tricky business. These tests are notorious for their false positives. That means that the test indicates you are allergic to something, but in fact, you are not. That can definitely be confusing for all concerned!

Types of Allergy Tests

Also, not all allergy tests are the same, so their results differ as well. The traditional type of allergy test is a skin test or scratch test. This kind of test has been around for decades.

It involves placing a drop of liquid consisting of a possible allergen, such as cat dander, on the skin. Then, the allergist scratches or pr.icks the skin to enable the solution to enter the skin.

If a red, raised itchy area called a wheal develops at the spot, it's a good sign that you may be allergic to that allergen. This is called a positive reaction.

Two other types of skin tests may also be done:

• Intradermal test, where the allergen solution is actually injected into the skin; often used to followup scratch testing.It's more sensitive, but also produces more false-positives.
• Skin patch test, where a pad impregnated with the allergen solution is taped to your skin for a day or two.

There are also blood tests that can be done to explore your allergy triggers. The most common is the RAST test, which checks for your levels of IgE, which is short from immunoglobulin E, an antibody associated with allergies. Other IgE tests are the ImmunoCAP, UniCAP, or Pharmacia CAP.

If your tests, whichever kind you have, are not negative, then your best bet is to discuss them with your allergy specialist. Each test may be interpreted slightly differently, so comparing numbers between them can be a bit like comparing apples to oranges.

But generally, the higher the number, the more sensitive you are to that particular allergen.