With the increasing incidence of food allergies, pediatricians need to be
prepared to recognize the symptoms, promptly initiate an evaluation, and educate
the family about the required emergency responses, if needed.
Food allergies in infants may present as atopic dermatitis, hives, vomiting,
poor weight gain, bloody stools, or swelling. Sometimes these symptoms are
reactions to the mother's diet, although the response is often to formula or a
number of foods that the child is beginning to consume. Severe eczema, even
without the other symptoms, may be sufficient to suspect food allergies. If an
infant has only mild eczema, however, food allergies usually are not involved.
A pediatrician's role
As the first step in evaluating suspected food allergies, a pediatrician needs
to elicit a detailed dietary history of both the infant and the mother if the
infant is still breastfeeding. The family should be asked to describe the most
recent reaction and the associated circumstances. The pediatrician should
ascertain the severity of symptoms, and inquire about the different foods that
may have produced an allergic response, the quantities of suspected foods that
tend to evoke symptoms, the timing between ingestion of a suspected food and
onset of symptoms, and whether symptoms occur with each exposure to a particular
food.
It is also important to determine the family history of allergies. When
family members have any type of allergy, a stronger possibility exists that the
child will develop allergies to foods. In such cases, the family should be
advised to delay introduction of common allergenic foods.
Infants who have had severe food reactions, such as respiratory distress,
hypotension, or loss of consciousness, need an immediate referral to an
allergist. Epinephrine must be prescribed if the history reveals risk factors
for life- threatening food allergy reactions – a previous life-threatening
reaction, allergies to peanuts or tree nuts, and an underlying history of asthma
(even without a peanut allergy). The family also needs to be taught how to
administer epinephrine and in which situations, to ensure a prompt response in
an emergency.
For less obvious cases of food allergies, with reactions that involve mostly
skin or gastrointestinal symptoms, elimination diets can be tried to identify
the food culprit. The child should avoid 1 suspected food at a time for at least
2 weeks to see if symptoms resolve.
An allergist's role
Allergy testing is used to confirm clinical suspicion of food allergy based on
the infant's history. It is important to note that in vivo and in vitro tests
are not diagnostic without a history of clinical reactivity.
After taking a careful history, an allergist will typically start a food
allergy evaluation of an infant with a prick/puncture skin test (PST) to assess
reactivity to suspected allergenic foods. The test yields results within 15
minutes, so the family can know very quickly which foods may be problematic.
During the skin test, a drop of a specific food allergen extract (based on
dietary history) is placed on the skin and the skin is punctured through the
drop. This technique requires specialized skill and practice to make results
reproducible. Application of positive and negative controls also ensures that
the skin is able to mount the response that is needed, but is not so sensitive
that it reacts to any physical stimulus.
PST results are fairly reliable when negative and almost always rule out
those foods as the cause of allergic reaction. More than half of positive
results, however, may be false. To make sure that the infant does not avoid
particular foods unnecessarily, CAP fluorescent enzyme immunoassay (CAP-FEIA) may
be used as a follow-up to positive skin test results.
CAP-FEIA is basically a blood test for detecting immunoglobulin E (IgE)
antibodies in relation to potential food allergens. Reliable diagnostic values
are available for a number of foods, such as egg, milk, peanut, and fish.
CAP-FEIA can be used for many additional foods, but reliable clinical cut-off
values are not available at this time. If the test reveals elevated IgE
concentration levels for specific foods, avoidance of these foods is considered.
When CAP-FEIA results are borderline, or if IgE is found to more than 1 food,
a food challenge may be necessary to make a definitive determination. Since food
challenges are labor-intensive and pose some risk to the patient, they are used
only when necessary to clarify the diagnosis and allergy status during long-term
follow-up.
Food elimination and challenges are also used to confirm the diagnosis for
some gastrointestinal food allergies that are not associated with IgE antibody,
such as dietary protein-induced proctitis/proctocolitis, dietary protein
enteropathy, and dietary protein enterocolitis. Infants with dietary
protein-induced proctitis/proctocolitis have blood and mucus in the stool, but
do not manifest vomiting or diarrhea. The diagnosis is usually made in the first
few months of age and typically the allergens are cow milk or soy proteins.
Dietary protein enteropathy may present as protracted diarrhea and vomiting that
may lead to failure to thrive. Cow milk protein is the most common trigger,
although the allergic reaction can also be to soy, cereal grains, egg, and
seafood. Dietary protein enterocolitis symptoms are similar to those in protein
enteropathy, but they are more severe and may progress to hypotension due to
hypovolemia. Cow milk protein, again, is the most typical cause, but other
triggers may include rice, oat, other cereal grains, and poultry. These food
allergy disorders usually resolve by ages 1 to 3 years.
To see whether the child is outgrowing the food allergy or if the allergy is
persisting, annual testing is performed with CAP-FEIA and food challenges, if
needed. If IgE values from the CAP-FEIA test are decreasing, the child may be
outgrowing the allergy to that food. If the IgE concentration in respect to a
given food is getting very low, a food challenge is conducted to check if the
allergy is completely outgrown. Increasing IgE values are a sign that the
allergy may be persistent, although this does not imply that the reactions are
getting stronger.
Conclusion
Primary care physicians are in a unique position to identify infants who may
have food allergy. Careful history is the first step in establishing the
diagnosis. By working with an allergist, the diagnosis may be confirmed and a
plan for long-term follow-up set to ensure successful management of food
allergies.
For Further Reading:
[1.] James JM, Burks AW. Food-associated gastrointestinal disease. Curr Opin
Pediatrics 1996;8:471-475.
[2.] Sampson HA. Food Allergy. Part 2: Diagnosis and management. J Allergy
and Clin Immunol 1999;103:981-989.
[3.] Sampson HA. Utility of food-specific IgE concentrations in predicting
symptomatic food allergy. J Allergy and Clin Immunol 2001;107:891-896.
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