Flawed Research

This is one of a series of several posts discussing issues that complicate the diagnosis of allergies. The summary and index of the series can be found here.

Problem: Studies that attempt to determine the prevalence and severity of allergies are often badly flawed.

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A woman I mentioned previously has anaphylactic allergic reactions to corn. This allergy sufferer took part in a study about the prevalence of corn allergy.

It was the Tulane study that's often quoted as the only definitive measure of the prevalence of corn allergy. My understanding is that the study was funded by corn companies.

All of the participants had positive skin prick tests and a clinical history of adverse reactions to corn. Of 22 people that fit the research criteria and agreed to participate, 3 were excluded from the study because of negative skin test results just prior to the test. Of the 19 remaining, 2 did not complete the challenge (perhaps because of the severity of their reactions?). Thus the study's conclusions were based on a pool of only 17 participants.

The researchers defined "allergic reaction" so tightly that they defined many clear typical allergic reactions right out of the study.

"If no objective reactions were observed at the end of the DBPCFC, open challenges were done with corn chips followed by popcorn. Subjects without reactions were considered negative."

Only about 6 or 7 of the 16 common symptoms of moderate to severe allergic reactions listed on Medline would have qualified under their standards. After all, itching, dizziness, difficulty swallowing, chest tightness, nausea and abdominal pain are not empirically observable or quantifiable.

Airway restriction was counted only if it resulted in more than a 15% decrease in peak airflow. Vomiting, diarrhea and congestion were, according to information from a participant, not considered a reaction at all.

The study summary says [definitions in brackets added by me]: "Five patients had positive challenges, two during the blinded portion, three with the open challenge. Reactions included: anaphylaxis, urticaria [hives], conjunctivitis [redness of the eyes] and rhinorrhea [runny nose], perioral urticaria [rash on the face or mouth area] and edema [swelling], and wheezing (>15% decrease in peak flow)."

(Incidentally, several of the ingredients in the study's placebo were also foods that often contain hidden corn (sugar often contains corn syrup, apple sauce and apple juice almost always contain corn-derived citric acid and/or corn-derived sweeteners, etc.), so I wonder if the placebo was truly a good control.)

The person I know who took part in the study says that she started vomiting within moments of the first administration of the test product, and the researchers considered that a non-reaction and continued the test. She spent the rest of the night huddled into a ball, crying from abdominal pain and having severe diarrhea and gastrointestinal distress. She got immediate mucus and congestion in her airways and sinuses as well.

Because of her history of anaphylaxis when exposed to popcorn fumes, she did not take the risk of participating in the open popcorn challenge.

The participant was categorized in the "no reaction" portion of the study results.

Vomiting and diarrhea are known, widely-accepted symptoms of anaphylactic allergic reaction, and yet these researchers and many doctors (including my own allergist) discounted them as allergic symptoms.

This participant said, "As a matter of fact, the nurse said I was definitely highly 'atopic' but was considered not reactive by their standard. Um... atopy is allergy."

If this is the kind of research we have, how accurate do you suppose the figures of allergy prevalence based on such studies (1-2% of adults, 6-8% of children) really are?