Objective. Adverse reactions following the ingestion of lactose have been reported in children with cow’s milk (CM) allergy. Whether this is attributable to the contamination of lactose with CM proteins is unknown. In this paper, we assessed clinical tolerance of lactose derived from CM whey in children hypersensitive to CM from 2 university hospital pediatric departments.

Design. Twenty-four children (5 girls and 19 boys, median 25 months old; range: 2–107 months) with immediate CM allergy confirmed at history or during double-blind, placebo-controlled food challenge (DBPCFC) were enrolled. DBPCFC with CM could be conducted in 11 of 24 patients. Children with a history of immediate/delayed reactions to soy formula (SF) were excluded. Clinical tolerance to CM, SF, and SF + lactose was assessed by: 1) skin prick test with casein, lactalbumin, soy commercial allergen preparations, fresh CM, SF, SF and lactose, lactose (Official Pharmacopoeia) in 4 concentrations (0.01%, 0.1%, 1%, 10%); 2) specific serum immunoglobulin E determination by CAP system technology; 3) DBPCFC in 8 incremental doses of SF + lactose and using SF as a placebo to make up a total of 240 mL of reconstituted formula.

Results. With a positive cutoff point of ≥3 mm wheal diameter at SPT, all patients were sensitized to fresh CM, lactalbumin, and/or casein. Twenty-three of 24 patients (95.8%) were SPT-positive to CM formula, 16 of 24 to lactalbumin (66.6%), 14 of 24 to casein (58.3%), and none to SF, SF + lactose, or lactose alone at all dilutions. Complexed immunoglobulin E determinations were positive for CM in 23 of 24 cases and negative in all cases for soy. Challenge with SF + lactose was negative in all cases.

Conclusions. Even children hypersensitive to CM are clinically tolerant to lactose and can safely consume foods and drugs with lactose from bovine sources as an ingredient. Lactose exclusion is unwarranted from soy preparations on grounds of potential allergic reactions to CM protein residue.

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