Incidence of Allergy in Children: Using Allergy Testing Panels (Pharmacia ImmunoCap) or Symptoms?

In the May issue of the Journal of Allergy and Clinical Immunology there is a very interesting article on the association (not cause) of childhood obesity and allergy by Dr. Cynthia Visness and colleagues (JACI 2009;123:1163-9). This study looked at over 4000 children between the ages of 2 and 19 years who participated in the 2005-2006 National Health and Nutrition Survey (NHANES). The survey asked specific questions about allergy symptoms. There was also an analysis for specific IgE antibody responses using a blood test. For background purposes the blood test (Pharmacia ImmunoCap) is commonly available and is being marketed to primary caretakers as a panel to help diagnose allergy. The study used a number of tools from epidemiology to look for associations between obesity and the presence of allergic disease. Their findings were that obesity in children may be a contributor to the increased prevalence of allergic conditions especially food allergy. However, I will not talk about the specific findings of that study at this time.

The study is very interesting and very well done. I was fascinated by not only their conclusions, but their inclusion of additional information on this large representative group of children. It is this ‘between the lines’ information that I want to go over in this report. I think that there are a few more points that can be made from the NHANES aside from the obesity/allergy issue.

Information, data for those scientifically oriented, is shown on 4,111 children. Each of these children underwent a blood study that looked for specific IgE antibodies to a variety of allergens. For the children over age 2 years but less than 5 years of age they were tested to a panel of allergens that included the following; house dust mites, cat, dog, cockroach, Alternaria (mold), peanut, egg, and milk. The children who were 6 years and older were also tested for IgE antibody to ragweed, ryegrass, Bermuda grass, white oak, birch, shrimp, Aspergillus (mold), thistle, mouse, and rat. Nine allergens were looked at in the younger group and 19 were evaluated in the older age group.

In addition to the blood tests questions were asked about previous diagnoses of allergic conditions such as hay fever, eczema, and allergies. Atopy (the condition in which someone makes an allergy antibody- IgE antibody) was defined as having any measurable IgE to any of the allergens tested for. An atopic child had at least one positive blood test.

In my opinion the NHANES methodology was very appropriate in being selective as to what allergens to test for. Note that the younger age group was not tested to tree, grass, or ragweed pollen. Also note that for both groups, the selection of foods was limited to a only a few.

This table is redrawn from Table 1.

 

Characteristic

Number

IgE

% Atopic

% Allergy Sym
Overall

4111

50.4

46.4

18.7
Age (years)

 

 

 

 

2-5

918

35.2

37.5

14.8

6-10

904

52.9

46.3

20.8

11-14

929

50.6

45.2

17.4

15-19

1360

59.2

52.1

20.6

 

What caught my eye was the difference between those who were given a diagnosis of allergy and/or who stated that they had symptoms of allergy versus the percentage of children who had one or more measure of atopy (allergic sensitization) by a blood test.  Only 18.7% of these children (overall number) had symptoms of allergy yet 46.4% (overall percentage) had one or more blood test that was positive thus fulfilled the criteria for atopy. The key question is why almost half of the population shows an allergy antibody yet only 20% have symptoms? The difference is not small between the two groups. Should we diagnose allergy by a set of symptoms due to exposures of a relevant allergen or dash the history and let the blood tests dictate the diagnosis and treatment. Almost 50% of the time that blood test panel will show a positive response.

What has happened here? Who is the allergic child? Does this blood test reveal too many false positive responses? Is it predicting an allergic future? Is it reflecting an allergic past? The result is not giving us a meaningful look at the current situation. I think this shows a significantly high level of falsely positive results.

My interpretation and what this side bar of the study has clearly shown is that the positive blood tests when done as a panel and done outside the context of a good history will yield clinically irrelevant information for a large number of children.

In the medical community of central Indiana there has been subject to very active marketing of allergy test panels (blood test, RAST). One of my referring pediatrician friends told me last week that an allergist from California came to town and visited primary care offices talking about allergy test panels on behalf of a sponsoring company. That reminds me of an old western- Paladin. The cowboy’s business card read ‘Have gun, will travel’.

The original purpose of the article is worthy of a future report and a watchful eye on how this association.

No pun intended, but food for thought?

Fred Leickly

June 6, 2009   Posted in: Allergy Testing

One Response

  1. Allergies: A Leickly Story » Blog Archive » Food Allergy among Children in the United States – Article Review - December 1, 2009

    [...] Blood tests for IgE antibodies to foods were taken from the National Health and Nutrition Examinatio…. Specific IgE antibodies to peanut, egg, and milk were measured using the Pharmacia ImmunoCap 1000 System. Specific IgE to shrimp was measured only in children over the age of 6 years. The range of specific IgE values was 0.35 to 1000 kU/L. [...]

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