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Responding to Criticism- Phadia Immunocap Testing

Since this blog’s inception in January 2009, I have received thousands of hits on the website. Some of the visits lead to questions and comments, either posted on the site or via email. I thoroughly enjoy the conversation and the opportunity to help families wade through what can be a very confusing specialty. Now, I have to deal with my first negative comment—and I understand that this is par for the course in the world of blogging.

 

The comment in question was posted to my October 15, 2009 entry titled Phadia Allergy Tests and Asthma .

 

The commenter disagrees with my interpretation feelings towards in-vitro testing. I am, in the commenter’s perspective, being self-serving by berating this type of allergy test in favor of high cost allergy skin tests that are “archaic”. The commenter also pointed out that it would be impossible for all 23 million patients with asthma to be seen by the 4,000 practicing allergists, and thus most asthmatics must be managed by the primary caretaker. The commenter points out that it is a disservice to disallow a patient to know the ‘root of their problem’–and in their practice, the immunocap is used daily to uncover the triggers that are causing symptoms. Mention is made of two studies in which allergists ‘…cannot guess sensitivities based on history or physical alone by more than 50%’. The comment ends with the commenter hoping that I and my allergy colleagues feel good about a futile and self-serving vendetta against in-vitro allergy testing. I was then challenged to talk about something called ‘allergy component’ testing.

 

There are quite a few issues here.

 

1. I use the Phadia Immunocap for IgE levels to specific foods. This is how we look for possible food allergy resolution. For many foods a specific concentration of specific IgE antibody is related to a risk of a reaction with exposure. We proceed with a food challenge based on the value of an in-vitro test. Without the in-vitro tests our practice would not have so many successes in outgrowing food allergies. IN-VITRO TESTS HAVE VALUE. I USE IN-VITRO TESTS.

 

2. I do have specific issues with in-vitro testing and that is the use of a PANEL. Too often the panel contains items that are not relevant (meaning there is no exposure to the allergen). The panel wraps a number of items and offers specific IgE at one price. Representatives from the ‘in-vitro testing industry’ recognize that this is an issue. However, by adding additional items a higher price can be justified.

      For example look at one Michigan hospital’s Phadia ImmunoCAP Food Allergy Panel - Clam, Egg White, Codfish, Corn, Milk, Peanut, Scallop, Shrimp, Soybean, Walnut, Wheat, and a total IgE. As individual in-vitro tests these can be $100 a piece. By the way, a skin prick test is about $10 per item. There clearly are a few foods on here that are not part of the usual diet- they are not clinically relevant. How many infants who have atopic dermatitis are eating scallops, shrimp, and clam? A food panel that contained egg white, wheat, soybean, codfish, peanut, and milk would be appropriate. A second panel with the shellfish and a third with the tree nuts would be very acceptable if used based on the food exposure history.

      A report by Anna Wetherbee in the journal Lab Medicine, November 2007 (Vol 38, no. 11 649-650)talks about the clinical appeal of in-vitro testing and the use of allergen panels. Interestingly, primary care physicians have been slow to embrace in-vitro testing partially due to a questionable total value proposition. The panel offers 15 or more specific allergens and billing for the panels is computed on a per allergen basis where the cost can be as much as $185 (Medicare fee schedule)

POINT- ORDER SPECIFIC ITEMS RELATED TO THE TIMING OF SYMPTOMS. AVOID PANELS.

     

3. The value of any allergy test is only as good as the history that supports it. The test makes no one allergic, it only demonstrates the production of IgE antibody which may or may not be relevant. They cannot be used to predict alllergy and the clinician needs to assess the clinical relevance of the test. Individual in-vitro allergy tests can do this. A set panel may not be appropriate for the seasonality of the patient’s symptoms. A simple example- if wheezing occurs August 15 and continues until the second frost then ragweed would lead the list of usual suspects. Of what use is the value for tree pollen given this history? A panel may obligate an analysis of other allergens that have no relevance and would add to the cost.

 

4. In-vitro testing overcalls inhalant allergy. Please see the results of the NHANES study(earlier posting in the blog ). This study involved a health survey of 4000 children and was published in a reputable journal. In this study the in-vitro test declared that almost 50% of the study population was allergic whereas by the children’s (parents’) history, only about 20% had symptoms of an allergic condition. The in-vitro tests are used extensively with our food allergy children and they are not as effective for inhalant allergy.

 

5. Intra-dermal skin testing is rarely done in our practice. The literature and evidence suggests that this type of test in most instances does not further the diagnosis.

 

6. If immunotherapy is considered, testing should be performed with the materials that are to be used in the immunotherapy extracts.

 

7. There are specific recommendations regarding when to refer to an asthma specialist. These can be found in Section 3 Component 1 page 68 of the 2007 National Heart, Blood, and Lung Institutes, National Asthma Education and Prevention Program, Expert Panel Report 3. There is no intention that every patient with asthma be seen by an allergist and clearly not every patient needs allergy testing. The use of allergy testing is considered within the context of severity and control with their subcomponents of risk and impairment.

 

8. I love to review articles. My training as a PhD student in pharmacology helped me learn the knack of critical review. My recent training in Public Health has added epidemiologic skills and insight to biostatistics. When I quote something it is always referenced so the reader can go to the source.

      There are two articles that have the batting average of an allergist at 500 for identifying a specific allergen by history or physical examination. I wonder, what was the gold standard in these studies? Remember, the best test for a trigger is a challenge. The history of seasonality or perennial exposures, symptom free days, and symptomatic days helps me sort out what I think is going on. The allergy tests help verify my clinical impression. Would you have the laboratory result determine the clinical impression or the history? Allergy tests can be falsely positive and falsely negative.

      The sensitivity of a test is the ability of the test to identify correctly those who have the condition of interest.

      The specificity of a test is the ability to identify correctly those who do not have the condition of interest (M.Szklo and F. Nieto, Epidemiology, Beyond the basics, 2nd edition).

      In many reviews of the in-vitro tests, the sensitivity is high and even up to 100% for some allergens (correctly identifying those who are allergic). However, the specificity can be as low as 50%, correctly identifying those who do not have the condition. The in-vitro test can identify who has sensitization, however there as a fair number identified as having allergy by the test, but do no have symptoms (false positive results). We have to careful on how the results are interpreted. 

9. The email address of the person who wrote these comments indicated an association with a particular health care organization. I wonder what their background is—a physician, a nurse or a nurse clinician, a researcher, or a laboratory worker? The health care group has at least two allergy practices within its coverage. I wonder what the credentials of the commenter are in this area.

 

10. I am not sure what allergy component testing is. I entered the term in a search engine and got no results. I would be most happy to talk about it if I knew what it was.

 

 

I use in-vitro testing, I use the Phadia system for IgE. It is an excellent test when used in the proper context. I do, however, have issues with the marketing of panels, including cost, confusion, interpretation, outcomes. The use of these panels has generated a good number of referrals. I have been significantly busier with children (parents) coming for explanations, apprehensions, and fears based on what a panel revealed.  In the long run, if I was asked to pick what the 4 most important allergens to evaluate they would be house dust mites (two species), cat (if the history supports), dog (if the history supports), and cockroach (also history dependent). The family could actually do something about these exposures.

Fred Leickly


November 13, 2009 · fleickly · 6 Comments
Posted in: Uncategorized

6 Responses

  1. Rebecca Cooley - November 24, 2009

    I am sorry your “commentor” was so critical. I thought you handled your reply very well. During our first few visits with you (for my daughter) I learned a lot about allergy testing which I didn’t know, and your answers all made perfect sense to me. One thing which really stood out was not to do the blood tests unless there was a good reason to do so ( a history of hives relating to a food, etc.)
    It’s okay for people to have differing opinions — that’s part of what makes life interesting — but use the Golden Rule (as you did).

  2. fleickly - November 29, 2009

    Thank you for the kind words.
    FEL

  3. Leslie - January 26, 2010

    I think that if the child/infant is breastfeeding then the full allergy panel including nuts and seafood is totally appropriate. My daughter was exclusively breastfed when I had her tested at 6 months and we found out that my eating nuts and milk was the cause of her discomfort and severe eczema. Skin test confirmed her allergy. When I eliminated those foods from my diet her skin cleared and she became a much happier baby.

  4. fleickly - January 26, 2010

    I am glad that worked for you and your child. You also point out the importance of the history of a food exposure-your ingestion of tree nuts and shellfish.

  5. Karim Mourabit Amari - July 11, 2010

    I think component allergy testing is the possibility to test if IgE against single epitopes of an allergen is. I am reading stuff about Immunocap and as an example, for peanuts, you would have components Ara h 1, Ara h 2, Ara h 3, Ara h 8 and they could be tested individually and the resulting profile can be interpretated. From what I understand at this stage, Ara h 1,2 and 3 are the most relevant components to test in regard to peanuts allergy.

    I have an article which is good : http://www.ncbi.nlm.nih.gov/pubmed/20146729

    IgE to peanut allergen components: relation to peanut symptoms and pollen sensitization in 8-year-olds.

  6. fleickly - July 11, 2010

    Given the crudeness of the diagnostic tests currently available for determining IgE to peanut, I think this new technology may help sort things out. I have been reviewing all the peanut positive children we have seen since January, 2009 to date. There are about 350 who have had a positive peanut skin test. Their histories of clinical reactivity range from anaphylaxis to contact urticaria to having no reactions at all (they have eaten peanut have had no problems, but have that positive test).
    I have seen that article. Thanks for referencing it and thanks for the comments.
    FEL