Please Don't Pass the Milk, Eggs, Peanuts, and Fish

We visited Charlee's allergist last week. After a whopping $700 (out of pocket) for testing, he reconfirmed her allergies to milk, eggs, peanuts, and fish. Her antibody levels for her allergies are all higher than a year ago:

Allergen (Last Yr / This Year)

• Milk (17 / 54)
• Egg (31 / 69)
• Peanut (5.6 / 5.9)
• Cod (- / 24.5) [we didn't test for fish last year because we didn't realize she was allergic]
• Tuna (- / 8.4)
• Shrimp (- / 0) [no allergy to shrimp, but because of risk of cross-contimation, she will avoid shrimp]
• Salmon (- / 3.4)
• Trout (- / 10.6)
• Tilapia (- / 66) [not surprised that this is so high since it's what she had a strong reaction to]
• Black bass (- / >20)

The allergist says it is normal for an infant to have low antibody levels followed by a spike in the next round of testing. He asked me not to read anything into the relative levels, but he also told me that they won't even attempt to re-introduce a food until the antibody level is less than 2.

For now, we continue status quo, avoiding all of those foods.

Here's a little more info on the allergy testing she had done (excerpted from the Food Allergy & Anaphylaxis Network).

What do the tests measure?

The tests determine the presence of IgE antibody directed to particular foods. (IgE is the allergic antibody that mediates most food allergy reactions.)

What types of tests are available?

Two commonly used tests are blood (CAP-RAST) and skin prick tests. The blood tests require a small sample of blood to be sent to a laboratory, where the amount of IgE antibody to the specific food is measured. The result is reported as a numerical value. ...

How are the tests interpreted?

The easiest test result to interpret is one that is negative; it is very unusual to have IgE-mediated reactions to a particular food when the skin or blood test to that food is negative.

Unfortunately, the interpretation of positive tests is not so straightforward. Positive tests indicate that IgE is present but do not, in isolation, prove that a reaction will occur upon ingestion of the food. In fact, people who "outgrow" their food allergy usually continue to have a positive test result to the food for many years....

Do the test results indicate the level of severity of a reaction?

Neither the size of the skin test reaction nor the level of specific IgE antibody in the blood test necessarily correlates with the type or severity of symptoms. Consider an allergy evaluation with a "2+" positive skin test and a positive CAP-RAST test to peanut. One person with these results may be eating peanut every day without symptoms, while a different person may experience anaphylaxis from peanut. Similarly, that second person may eperience only an itchy mouth on one occasion, anaphylaxis on another, and a mild case of hives on yet a third occasion of peanut exposure.

The level of specific IgE antibody measured using a particular method of RAST test (CAP-RAST FEIA uses units called kUA/L, which indicate a concentration of specific IgE) was recently reported to be useful in determining the chance of true reactivity to certain foods. For example, an IgE antibody level of more than 7 kUA/L to egg, more than 15 to milk, more than 14 to peanut, and more than 20 to codfish was highly predictive (greater than 95 percent chance) of providing some type of allergic reaction among highly allergic children. Unfortunately, lower values, unless virtually undetectable, may still indicate a potential for having an allergic reaction. This test may prove useful in following levels of particular IgE antibodies over time to see if they are falling (perhaps indicating that the allergy is being outgrown).

As you can see, the interpretation of these tests can be quite confusing. Your doctor must always interpret these tests in the context of the individual medical history. Even the selection of which foods to test must also be decided carefully and in the context of the medical history, since up to one-half of positive tests may not accurately reflect an allergy. Lastly, like any test in medicine, the results are occasionally wrong and should be repeated if an error is suspected.