July 22, 2003

PHILADELPHIA (American Association for Clinical Chemistry) -- There is public confusion regarding our body's reaction to certain foods. On a basic level, an adverse food reaction refers to any reaction following the ingestion of a food. One cause might be a food allergy, the result of an abnormal immunologic response following the ingestion of a food; the other reaction might be the consequence of food intolerance, caused by a non-immunologic mechanism.

Sorting out the causes, diagnoses, and treatments of food allergies in children is Wesley Burks, M.D, a leading researcher in the area of food sensitivity, who has focused on allergies to peanuts and soybeans. A professor and head of the Division of Allergy and Immunology in the Department of Pediatrics at the University of Arkansas for Medical Sciences (UAMS), Dr. Burks will make his presentation on "The Challenge of Food Allergies in Children" at the 55th Annual Meeting of the American Association of Clinical Chemistry (AACC) being held July 20-24, 2003, at the Pennsylvania Convention Center in Philadelphia, PA. More than 16,000 attendees, are expected.

Background

When the body's immunologic response to certain foods is not a factor, then other causes must be considered. The food might be toxic, caused by bacterial poisoning, heavy metal poisoning, or selected fish poisoning. Non-toxic factors include lactase deficiency, gallbladder/liver disease, anorexia, and pancreatic insufficiency. An abnormal immunological response can have responses that are IgE mediated (oral allergy syndrome, analphylaxis) or non-IgE mediated (protein-induced enterocolitis).

The Cause of Allergens

Allergens are characterized by proteins (not fat/carbohydrate) with 10-70 kD glycoproteins that are heat-resistant and acid-stable. Major allergenic foods (>85 percent of allergy) in children are milk, egg, soy, and wheat; among adults, peanut, nuts, shellfish, and fish may cause the problem.

When Allergies Kill

Food-induced anaphylaxis (an immunologic (allergic) reaction characterized by contraction of smooth muscle and dilation of capillaries due to release of pharmacologically active substances (histamine, bradykinin, serotonin, and slow-reacting substance)) can be indicated by rapid-onset, multi-organ system involvement, and is potentially fatal. The foods most responsible for this condition are peanuts, nuts, and seafood. In America, more than 100 deaths each year occur from peanut/nuts/shellfish.

Non-lethal Allergic Responses to Food Most responses to food are not fatal. They include the oral allergy syndrome whereby an allergic (immunologic) reaction to certain proteins in some fruits, vegetables and nuts, develops in some people with pollen allergies. This is referred to as an oral allergy syndrome because it usually affects the mouth and throat. The other is known as pediatric gastrointestinal syndromes and are associated with migraines, behavioral/developmental disorders, arthritis, seizures, and inflammatory bowel disease.

The Extent of the Food Allergy Problem

The public believes that some 20-25 percent of people have food allergies. In reality, the numbers are much lower, with one to two percent of adults having this reaction and six to eight percent of infants/children having such response. Among adults, the most severe response is to peanuts and tree nuts. Among children, the offending food item is primarily milk.

Diagnosis in Children

The first step in addressing possible food allergies in a child is a complete diagnostic work-up consisting of the following:

• History/Physical: The parent will have to have a history of the disorder including symptoms, timing, reproducibility and whether the condition presents acute reactions or resembles a chronic disease. The parent should have diet details or a symptom diary listing specific causal food(s) and any possible "hidden" ingredient(s). This will be followed by a physical examination to evaluate disease severity. The clinician will then identify the general approach; namely, allergy vs. intolerance and IgE versus non-IgE mediated.

• Diagnosis: Laboratory Evaluation: If the condition is suspected of being IgE-mediated, then prick skin tests or RAST (or a fresh extract in the case of an oral allergy) will be performed. If the diagnosis is suspected of being non-IgE-mediated, a biopsy of the gut or skin will be considered.

• Interpretation of Laboratory Tests: The positive prick test or RAST indicates the presence of the IgE antibody, not clinical reactivity (~50% false positive). A negative prick test or RAST essentially excludes IgE antibody (>95 percent).

Diagnostic Strategies

When food-specific IgE concentrations predictive of clinical reactivity are present, then the following could be recommended:

• Elimination diets eliminate suspected food(s), prescribe a limited "eat only" diet, or offer an elemental diet. This diet usually lasts between one and six weeks.

• Oral challenge testing (physician supervised, with emergency medications available) can be open, single-blind, or double-blind, placebo-controlled. If the results indicate an IgE-mediated allergy, then the test for specific-IgE antibody could be negative (thus, reintroduce food) or positive (start the elimination diet). If the elimination diet provides no resolution, then reintroduce the food.

• The diagnostic approach for non-IgE-mediated disease includes disease with unknown mechanisms, such as food additive allergy. Elimination diets may be called for, and parent should search for hidden ingredients (peanut in sauces or egg rolls), labeling issues ("spices"), cross contamination (shared equipment), and "code words" (such as "natural flavors"). A registered dietitian should also be consulted.

Treatment

For the newborn, substitute infant formulas may be called for. These options include soy (after confirming that soy is IgE negative), cow's milk protein hydrolysates, partial hydrolysates (those which are not hypoallergenic,) and amino acid-based formulas that lack allergenicity.

In the case of emergency treatment, epinephrine is the drug of choice for an emergency response to reactions. A self-administered epinephrine is readily available and patients can be trained to self-administer this medication. Antihistamines can be a secondary therapy. It is also beneficial for the patient to have an emergency plan in writing, available to schools, spouses, caregivers, mature siblings and friends. An emergency identification bracelet is also advisable.

Strategies for Prevention

If there is a positive family history for food allergies, then the first prevention steps should take place at birth. As breast feeding is generally protective of allergy, efforts should be made to wean/supplement with extensively hydrolyzed hypoallergenic protein hydrolysate. Most importantly, the infant should have at least a six month delay in consuming solid foods; should be between six and 12 months old before consuming cow's milk and dairy and products; be between 12-24 months old before being offered eggs, and be between 24-28 months of age before peanut, tree nut, and seafood is introduced.

Conclusions

In considering pediatric food allergies the parent must remember that a history and physical examination are paramount; IgE and non-IgE associated conditions exist; diagnosis is performed by elimination and challenge; avoidance/education/preparation for emergencies are current therapies; and periodic re-challenge to monitor tolerance as indicated by history, allergen, and level of food specific-IgE.

The Telangana Science Journal, July 2003