Critically Reviewing the Literature on Food Allergy

Diagnosing and Managing Common Food Allergies: A systematic review.

This week I am presenting at a seminar at the Riley Child Care Conference. The seminar was the idea of Dr. Sandeep Gupta (pediatric gastroenterology). The title is “Puzzling, Perplexing, Problematic Allergies in Children”. The third lecturer is Dr. Jeff Travers (dermatology). I have the task of talking about allergy testing and referral to the allergist. Food and specifically food allergy is the common ground for the three specialties. My focus will be on food allergy evaluations and management.

I have been putting this presentation together for a number of weeks. I was ahead of deadline and sent my slide copy and handouts to the organizers for inclusion in the syllabus. For those involved in continuing medical education (CME) programs, that is what is called being a good citizen. However, I just changed major parts of my talk due to the appearance of an article in the Journal of the American Medical Association (JAMA) this past week. The article is entitled ‘Diagnosing and Managing Common Food Allergies: A systematic review’ by J Schneider Chafen and colleagues (JAMA, May 12, 2010- Vol 303, No 18, pages 1848-1856). I know that I am in trouble for doing this because showing slides that are not part of the syllabus has always been a most dangerous behavior for a CME speaker. The audience tends to yell at the speaker for this violation, however I will take the hits in favor of providing the most up to date information.

The idea of a ‘systematic review’ is a very specific and intense look at the literature on a specific topic. First a few basic questions are established. This is followed by an extensive review of everything in the literature on the topic/question. There are strict inclusion criteria. The data from the studies is abstracted, the quality of the study is assessed, and the data is then synthesized. The hope is that those studies which have substantial numbers of cases in randomized controlled studies were evaluated and included in the review. This is done to present the best, the most valid, and most convincing work.

This systematic review caused me to revise my talk and add seven slides that will truly reflects the most current information.

This review was sponsored by the National Institute for Allergic and Infectious Diseases (NIAID). It is the prelude to the establishment of National Food Allergy Diagnosis and Management Guidelines, a topic I have talked about previously. There were 12,378 literature citations on food allergy found between the January 1988 and September 2009. From this, only 72 articles qualified for this review. That represents approximately 0.05% of the starting total. This is important to note. Almost all of the articles pulled did not fit the purpose of this review. The specific topics that were sorted inclluded; food allergy prevalence, studies of diagnostic tests, and studies on management and food allergy prevention. Further restriction involved looking at studies that dealt with specific food allergies; milk, egg, peanut, tree nut, fish, and shellfish (50% of all food allergy).

The overall summary was that the literature/evidence regarding food allergy prevalence, diagnosis, and management is voluminous, diffuse, and according to this review is also critically limited by the lack of uniformity on what food allergy is (lacking uniformity for criteria for the diagnosis of food allergy). The point is that when looking at an article on food allergy we have to be sure what is being talked about. All too often the diagnosis is based on laboratory study results alone. This lack of defining food allergy has severely limited making conclusions regarding the best practices for managing and preventing food allergy.

It may come as a surprise, but food allergy has no universally accepted definition. The NIAID suggested definition is “an adverse immune response that occurs reproducibly on exposure to a given food and is distinct from other adverse responses to food, such as food intolerances, pharmacologic reactions, and toxin-mediated reactions.

The results were as follows;

Prevalence- food allergy affects more than 1-2% of the population but less than 10%.
Diagnosing- food challenges, skin prick tests (SPT), & serum food-specific IgE (blood tests for food allergy) all have a role in making the diagnosis, but no one test has sufficient ease of use or sensitivity or specificity to be recommended over the other tests. The food challenge suffers from not being easy to use in general clinical practice.
Management (elimination diets)- only 1 randomized controlled trial (RCT), established as the more scientifically rigorous test, was identified for the effect of elimination diets. RCT are generally lacking for atopic dermatitis and eosinophilic espophagitis. The benefits for elimination diets are uncertain based on published evidence, and potential benefits need to be weighed against the potential nutritional risks especially in children. It is important to point out that this is not referring to trials for serious life-threatening food allergy reactions, such a trial would be unnecessary and unethical.
Immunotherapy- not a currently licensed method for treating food allergy. May be effective in generating desensitization. The effect on long-term tolerance needs to be determined.
Prevention- In high-risk infants hydrolyzed formula may prevent against cow’s milk allergy, but standard definitions of high risk and hydrolyzed formula do not exist.

There were a few general comments made that are worth noting.

There is the potential for the over-diagnosis of food allergy
Consequences

Dietary restriction

Nutritional problems

Anxiety/worry

Social challenges due to food allergy

There were a few final comments in this paper that are worth consideration.

Proper interpretation of SPTs and serum food-specific IgE results requires evaluation of the data within the context of the clinical history and physician understanding of symptoms consistent with clinical food allergy to separate true positives for food allergy.
The over-diagnosis or misdiagnosis of food allergy by medical practitioners obscures the substantial morbidity caused by patients truly affected by immune-mediated food allergy and serves to perpetuate some public misperceptions that food allergy is a trivial medical condition.

We all have a significant amount of work to sort this all out. The first steps are coming to some consensus as to what a food allergy is and what it is not. We then need to perform a detailed medical history to tease out a reproducible immune response with exposure to a food. Next we need a diagnostic tool or tools to be used to confirm our impression. The food challenge has been the gold standard for this, however it is not easy to perform food challenges. The next need is a plan of management. There has always been avoidance. We can add ‘Father Time’ as some food allergies can be outgrown. We eagerly look forward to immunotherapy that not only provide desensitization but will lead to tolerance.

FEL

May 16, 2010 · fleickly · No Comments
Tags: Food Allergy, Food Allergy Epidemiology, Food Allergy Testing · Posted in: Allergy Testing, Food Allergies