Allergies: A Leickly Story » Peanut Allergy

Peanut Allergy Misdiagnosed in 2 out of 3 Cases ?

fleickly — Sun, 25 Apr 2010 18:10:44 +0000

Attacking Peanut Allergy

Peanut Allergy Misdiagnosed in 2 out of 3 Cases

This title from Medical News Today April 13, 2010 caught my attention. It has always been a mystery as to why peanut allergy has increased dramatically over the years. This publication may shed some light on that mystery.

There are a number of factors in the peanut allergy equation and a recalculation may be necessary. First we need to be careful in discerning peanut allergy from peanut sensitization. Peanut allergic children would be those who have symptoms with exposure and evidence of a positive allergy test (skin prick test or specific IgE to peanut determined by a blood test). The sensitizated child is one with a positive test and no clinical correlate.

Secondly, the use of allergy tests has become more frequent and is being done by many other specialties. The manufacturers of blood tests for allergy market to primary caretakers an array of food allergen diagnostic panels that contain peanut along with many other foods. If the history was hives occurring after eating egg, a panel would include egg but would also have a number of additional foods. Sometimes these add-on foods return as positives (despite no history of a problem with ingestion) and the diagnosis of allergy is made.

Thirdly, this news report indicates that the diagnosis of peanut allergy was wrong in 66% of the patients.

A reworking of the prevalence of peanut allergy has a potential confounding variable; faulty diagnostic tools.

This news article began with a poignant comment- peanut allergy has always been associated with a deep anxiety, especially in the parents of peanut allergic children. I have many patients who will attest to that.

“Many people are being told that they are allergic to peanut, that they must avoid them and all foods that contain them at all costs, are actually not allergic to the nut at all” says Professor Wickman (Stockholm, Sweden). Dr. Wickman reported that 2/3 who are considered allergic to peanuts experience mild symptoms or none at all. A cross-reactive protein from birch tree pollen was thought responsible for the peanut reaction.

This report included the shortcomings of the materials used for allergen skin testing and those used for testing the blood for allergy.

To address this issue, a new diagnostic test was used on 4000 children to determine the specific proteins that are cross-reactive. It is known that specific peanut proteins are responsible for allergic reactions to peanut. The new test looks at antibody (IgE) production to the allergy-causing proteins. This allergy component test was used to show that 2/3 children who were diagnosed with peanut allergy were not allergic. Their positive test to peanut was due to some other protein that cross-reacted.

Now this was a news report and not a peer-reviewed article and I know how reporters can get things wrong or misquote. In regards to the report, remember peanut is a legume, not a nut.

In the report a statement is made that…” up to 7.5% of children seemed to be allergic to peanut at age 8 based on routine tests”. This made me wonder if they were truly allergic (symptoms by history) or they were declared allergic because a test was positive (done routinely for allergy?).

Now for a few critical comments- both positive and negative;

1. The capability of sorting out reactivity to the important proteins is applauded. We may be able to go back and de-diagnose a seemingly large proportion of peanut allergic people. The peanut-free tables at the schools are still essential but will be smaller by 2/3.

2. How would this been all different if the diagnostics, both skin prick tests and specific IgE would have been done only in those who had a history of exposure and reactivity with exposure? If the patient’s history directed our choice of individual tests, would we have so many peanut sensitive/allergic people? Avoid doing food allergen panels. Pick out the pertintent allergens- it will be less confusing and it will save money (one example from a local sendout laboratory -$300 for the panel and $25 for the individual allergen).

3. Look at the consequences of marketing panels or doing standard groupings of skin tests or blood tests- in 66% diagnosed perhaps falsely the families have an emotional burden, a nutritional burden, an isolation burden, and a financial burden. The peanut allergic person needs to have self-injected epinephrine available.

4. We always have to be careful in applying the findings from one area to another. This report on the 4000 children was from Sweden. There may be significant differences in our population. I would relish the opportunity to sort out our population of peanut sensitive children.

I am an advisor to the Southside Indianapolis Food Allergy Support Group. In March when I presented an update on food allergy, I promised that I would look at our peanut positive population. This has been quite a task. I am creating a database to characterize the population in the hopes of being able to participate in a peanut study. We have 360 positive skin tests for peanut from January 1, 2009 through March 31, 2010-15 months of clinic visits. The spreadsheet has a number of epidemiologic parameters including the age and type of reaction to peanut. Many of the children were diagnosed based on a panel that was performed because of atopic eczema or due to blood test panels and referred by primary caretakers for further evaluation. A few had anaphylaxis.This project is fascinating and I think will be very informative. It hopefully will catch the eye of those in the allergen diagnostic community or someone looking for a large population to enroll in a peanut immunotherapy study. These families are highly motivated to make a difference and to help others with this problem.

The new technology may help to address a historical and continuing over-enthusiastic and unfocused use of allergy tests, both skin prick test and blood test for peanut allergy. The tests we have now only tell us that antibody (IgE) is being made. The significance of that antibody is left to the clinician and must be based on the history and exposure to the allergen making sure that the clinical condition fits the template of IgE-mediated reactions. I for one eagerly await the arrival of more definitive diagnostic tools.



FEL

Peanut Allergy vs. Peanut Sensitization

fleickly — Sun, 24 Jan 2010 18:17:07 +0000

Allergy or tolerance in children sensitized to peanut: Prevalence and differentiation using component-resolved diagnostics.

N. Nicolaou, M Poorafshar, C Murray, A Simpson, H Winell, G Kerry, A Woodcock, S Ahlstadt, and A Custovic. Journal of Allergy and Clinical Immunology(JACI) 2010;125:191-7.

This article appeared in the most recent JACI. Almost as soon as I read the article, I began to put together this review (I am excited about the approach and ideas in this work). This paper states very clearly the problem of positive allergy tests for peanut (sensitization) and demonstrating clinical relevance- that is allergy to peanut. It addresses this problem using a new test for determining sensitization, component-resolved diagnostics.

Background:

A few very important facts are noted about peanuts;

1. Peanut is a nutritious and inexpensive food

2. Peanut is one of the most common food allergies

3. The prevalence of peanut allergy is increasing

4. Peanut allergy is usually life-long

5. Peanut avoidance is the current management of this allergy

6. Accidental peanut exposure is common

7. Peanut exposure in the allergic child can be life-threatening

Peanut allergy diagnosis issues:

1. An accurate diagnosis is very important- sensitized or truly allergic?

2. The gold standard for the diagnosis of peanut allergy is the

‘double-blind placebo-controlled food challenge (DBPCFC)

3. DBPCFC are costly, time consuming, and dangerous

4. The diagnosis is made with a suggestive history of what happens after exposure,

supported by a skin prick test or by the determination of specific IgE in the blood

5. These tests detect the presence of antibody (sensitization)

6. Positive allergy tests does not equate to the presence of allergic symptoms after exposure-

known as clinical allergy

7. Current tests –both skin prick tests (SPT) and specific IgE tests (sIgE-blood) use crude peanut

extracts and contain a mix of the allergic proteins and non-allergic proteins that may

cross-react with other allergens.

8. Bottom line- peanut sensitization may not equal peanut allergy

Solving this problem:

1. A new blood test to detect antibody production by the child to the important proteins in peanut that cause

allergic symptoms has been developed

2. This is called component-resolved diagnostics (CRD) – developed by Phadia

3. This may be a more accurate tool to assess food allergy (vs. sensitization)

The purpose of the paper was to look at the CRD to correctly identify children with peanut allergy.

Methods:

A birth cohort of children enrolled in the Manchester Asthma and Allergy Study (Manchester, England) was evaluated. Information on exposure and reactivity to peanut was collected. Peanut sensitization was measured by skin prick testing and by Phadia specific IgE.

There were 110 children (cohort contained 1085) who were sensitized and were asked to undergo a more extensive evaluation of their reactivity to peanut. This included more extensive history, skin testing, specific IgE, a DBPCFC, and the CRD.

The definition of peanut allergy included two very specific sets of criteria.

1. Sensitization and a positive oral challenge or

2. A convincing history and specific peanut IgE >15 kU/L and/ or a skin prick test that was greater than

an 8 mm wheal (this group did not have an oral challenge).

Results:

The cohort included 1085 children, 1029 were evaluated at age 8 years. There were 17 (1.6%) who had a history of peanut allergy.

Skin-testing was performed in 919 of the children with 47 (5.1%) having a positive SPT. Sensitization to grass pollen was noted in 59.6% of the children.

Blood studies were performed on 582 children with 71 (12.2%) having a detectable level of specific IgE to peanut. Grass sensitization was found in 67 (94.4%).

Overall, of the 933 children who had either a SPT or sIgE 110 or 11.8% were considered to be sensitized to peanut.

From this group of 110, 108 agreed to participate in the program. Seventeen did not consent to a food challenge. From the remaining 91 children, 12 had convincing histories and SPT/sIgE criteria to fit the definition of peanut allergy. Food challenges were performed in 79.

In the 79 oral food challenges to peanut, 66 had no symptoms with the exposure. Of the 13 who developed symptoms, 7 had two or more signs/symptoms and were declared peanut allergic. The breakdown on these number was- 66 were peanut tolerant and 19 were had peanut allergy (12 not challenged plus the 7 with a positive challenge).

The proportion of children with peanut allergy among those sensitized was 22.4%.

Peanut allergic and peanut tolerant children were compared.

1. Asthma, eczema, and food allergies were more common in the peanut allergy group.

2. Allergic rhinitis was more common in the peanut tolerant group.

3. Peanut tolerant children had lower peanut sIgE and higher grass sIgE.

The CRD results differentiated the peanut allergic from the peanut tolerant group. The peanut allergic group had higher values to the major peanut proteins Ara h 1-3. The peanut tolerant group had higher reaction values to grass components. The response to the peanut protein Ara h 2 was the best discriminator.

A model was developed to discriminate between children with peanut allergy and peanut sensitization. The model misclassified only 2 (6.9%) with peanut allergy and 4 (7.7%) peanut tolerant children.

Conclusions:

The majority of children who have peanut sensitization based on SPT or sIgE do not have peanut allergy. The CRD may help the diagnosis of peanut allergy.

Reviewers Comments:

This is exciting work. In the practice of allergy we struggle with positive tests and their clinical relevance. The authors very clearly point out the differences between sensitization and allergy. The test makes no one allergic. The test only tells us that specific IgE is being made. The history and/or a food challenge help define that clinical relevance in making the diagnosis of food allergy.

Phadia has developed a very specific assay which will help in making the diagnosis of peanut allergy. I am excited about the prospects for CRD. Phadia’s science is at the cutting edge of food allergy and I look forward to using this assay for the large number of children we see in our practice with a positive test for peanut antibody. I have always had the greatest respect for Phadia’s science; it is the marketing part that I have issues with (topic of a few of my posts).

The authors point out the strengths of this study. They performed a very extensive evaluation and used the DBPCFC for verification.

The small number of children reported is a recognized weakness. The authors encourage replication of their work.

The study looked at 8 year old children. I wonder about why that age and from the paper my guess is that this was the most recent year of evaluation on their cohort. This birth cohort attended the clinic at ages 1, 3, 5, and 8 years. In our clinic we use age 5 as our cut-off for peanut challenges. At this age, most children are able to communicate with us regarding the subtle aspects of allergic reactions.

Look at the rate of positive tests for peanut. The testing of a population of children revealed that almost 12% will have a positive test for peanut.

The last paragraph in the paper goes as follows; “The majority of children within the general population with positive skin test or measurable serum IgE to peanut do not have clinical peanut allergy.