Cow’s milk allergy is relatively common in babies (1:50) but rarely develops after one year of age. Symptom improvement on a cow’s milk-free diet and recurrence of symptoms with reintroduction of cow’s milk formula is the most accurate diagnostic procedure. Cows milk allergy may be underdiagnosed as it is common (but misguided) practice amongst UK GP’s and Paediatricians only to perform food allergy testing in children once they are 4 years or older.
Skin prick tests using fresh cow’s milk and RAST blood tests for cow’s milk protein IgE antibodies are the only reliable tests and have 60-90% accuracy. The whey (liquid) fraction of milk tends to cause most allergies, but the casein (curd) fraction triggers more severe and persistent allergies.The higher the milk-specific IgE level, the more likely there will be a clinically relevant milk allergy. High levels of Casein specific IgE antibodies indicate a higher risk for severe cows milk allergy and also for persistent cows milk allergy, On the other hand, IgG antibody testing for cow’s milk proteins (casein and b-lactoglobulin) is of no allergy diagnostic value and merely indicates exposure.
The clinical history and observation of the infant feeding are very helpful, and a family history of atopy increases the likelihood of a food allergy. Cow’s milk allergy can manifest with immediate urticaria and facial angioedema and respiratory, oral and laryngeal symptoms, as well as deteriorating eczema in addition to typical intestinal symptoms such as vomiting, diarrhoea, persistent reflux, food refusal and even anaphylaxis in severe cases.
Mildly milk-allergic infants often tolerate small amounts of processed dairy produce such as yoghurt and cheese as well as Goat’s milk. Infants with severe cow’s milk allergy will react to any traces of milk protein in partially hydrolysed milk formula, cooked foods and even breast milk, as well as any skin contact with milk proteins.