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What do you know about cow's milk allergy?

Elaine Linnane
BSc(Hons)
Managing Editor
Nursing in Practice

When a baby has cow's milk allergy they can react to a number of proteins in cows' milk, either passed through the mother's breastmilk from dairy products she has eaten, or from cows' milk, or formula based on cow's milk, given to the baby.
Symptoms of milk allergy are often mild and usually present in one or more of the three organ systems-gastrointestinal, respiratory and cutaneous. The symptoms will depend on whether the child has a rapid-onset reaction or a slow-onset reaction:

  • Rapid-onset reactions appear quickly - one minute to an hour after ingestion of small amounts of milk. These IgE-mediated symptoms include wheezing, vomiting, hives, anaphylaxis and angio-oedema.(2)
  • Slower-onset reactions are more common. Symptoms can take several hours or days to develop and include loose stools, vomiting, diarrhoea, colic/irritability, wheezing, skin rash and failure to gain weight.(3)

Diagnosing food allergy and intolerance
A thorough patient history and physical examination are required to identify the most likely mechanism of the disorder (ie, IgE-mediated or non-IgE-mediated) and identify the suspected food or foods.
The physical examination should concentrate on the cutaneous, respiratory and gastrointestinal systems. The general nutrition status of the patient and any physical signs of underlying nonallergic disorders should be noted. Patients experiencing severe atopic dermatitis or asthma should prompt a more aggressive evaluation.
IgE-mediated food allergies are usually immediate in onset, requiring only a small quantity of the food to be ingested, enabling rapid identification of allergenic foods. Non-IgE-mediated food allergies are usually slower in onset, taking up to 48 hours, and larger volumes of food are required, so the identification of suspect foods is often difficult.
If symptoms suggest IgE-mediated food allergy then it is appropriate to perform simple tests such as skin prick tests or radioallergosorbent tests (RAST).
The skin prick tests identify the foods to which the patient raises IgE. Radioallergosorbent tests are then used to quantify the food-specific IgE antibodies and determine the likelihood that they would lead to a clinical reaction. Suspected foods may then be eliminated, and challenge procedures are used to confirm the reaction.
If the process involved is non-IgE-mediated it may be more appropriate to proceed to a formal and structured elimination process before other tests are performed, but there is increasing interest in the atopy patch test (APT) in the diagnosis of food allergy in children: patch testing involves prolonged contact of the allergenic extract with intact skin under occlusion for 48 hours.

Management of cow's milk allergy
Currently the only treatment for cow's milk allergy is total avoidance of cow's milk proteins (see Figure 1).
Initially, if the infants are breastfed, a strict elimination of the causal protein from the diet of the lactating mother should be tried. If symptoms do not resolve or the infants are bottlefed, cow's milk substitute formulas are used to provide the infant with a complete source of nutrition, which does not provoke immune-mediated symptoms.
Cow's milk substitutes include soybean formulas and hypoallergenic formulas based on hydrolysed proteins and amino acid-based formulas. However, between 40% and 60% of infants with cow's milk allergy are also allergic to soy milk./(2) 
In some countries, milk from other animals such as goats, sheep and mares has traditionally been used for patients with cow's milk allergy. But other species' milk is not recommended for treatment of infants with cow's milk allergy - these milks are not nutritionally complete, are poor sources of certain vitamins (especially folic acid and vitamins B6, B12, C and D) and are only tolerated in a handful of infants with cow's milk allergy.
Since 25 November 2005, food labelling rules require prepacked food sold in the UK, and the rest of the European Union, to show clearly on the label if it contains milk or any of the ingredients of milk. This applies to milk from sheep, goats and buffalo, as well as cows.

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References

  1. Sicherer SH. Review: food allergy. Lancet 2002;360:701-10.
  2. Hill DJ, et al. Clinical manifestations of cows' milk allergy in childhood. II. The diagnostic value of skin tests and RAST. Clin Allergy 1988;18:481-90.
  3. Sampson HA. Update on food allergy. J Allergy Clin Immunol 2004;113:805-19.
  4. Høst A. Cow's milk protein allergy and intolerance in infancy. Pediatr Allergy Immunol 1994;5:1-36.