Immediate allergic reaction to lactose in a child with cow's milk allergy

Abstract

Lactose contains only trace amounts of cow's milk protein but, in rare cases, children with cow's milk allergy experience an immediate allergic reaction to lactose present in processed foods. Here, we report the case of an 11-month-old milk-allergic child, who tested positive for lactose by an oral challenge test, suspected of undergoing an immediate allergic reaction to lactose contained within Chinese soup. Her medical history revealed an outbreak of hives at 8 months of age after eating a small amount of yogurt. Blood tests revealed high levels of milk-specific IgE and she was diagnosed with cow's milk allergy. Her parents were advised to completely exclude cow's milk and dairy products from her diet. However, after eating Chinese soup for the first time at nursery school, she presented with urticaria and hoarseness at our emergency department. We performed an oral challenge test and the result was positive for lactose of pharmaceutical use. Patients with cow's milk allergy rarely experience an immediate allergic reaction to lactose, so such patients are not generally advised to avoid lactose. When patients are suspected of having lactose-induced symptoms, it is important to confirm this intolerance by an oral challenge test. If a positive result is obtained, patients and their families should be advised about the lactose-containing foods and medicines to avoid.