Allergy to cow's milk proteins: what contribution does hypersensitivity in skin tests have to this diagnosis?

Food allergy is an immunologically mediated adverse reaction to food protein. Cow's milk protein allergy (CMPA) is the most frequent type and is the one that is most difficult to diagnose. This study had the objective of analyzing the accuracy of hypersensitivity and specific IgE skin tests among children with CMPA and predominantly gastrointestinal clinical manifestations. The participants in this study were 192 children aged one and five (median of 2 yr). Among these, 122 underwent open oral challenge to the suspected food. After evaluating the sensitivity, specificity and positive and negative predictive values (respectively, PPV and NPV) of skin and specific IgE tests in relation to the gold standard (open oral challenge); all the children underwent the skin prick test (SPT), specific IgE test and atopy patch test (APT) for cow's milk, eggs, wheat and peanuts and the open oral challenge for the food to which the child was sensitive or had suspected sensitivity. Presence of food allergy was confirmed for 50 children (40.9%). Among these cases, 44/50 (88%) were of allergy to cow's milk protein. Children who presented a positive response to an oral challenge to cow's milk protein were considered to be cases, while the controls were children with negative response. Twenty-two of the 44 cases (50.0%) presented symptoms within the first 4 h after the challenge. The SPT presented 31.8% sensitivity, 90.3% specificity, 66.7% PPV and 68.4% NPV. The APT presented 25.0% sensitivity, 81.9% specificity, 45.8% PPV and 64.1% NPV. The specific IgE test presented, respectively, 20.5%, 88.9%, 52.9% and 64.6%. Despite the operational difficulty and the possible exposure risk, oral challenge is the best method for diagnosing CMPA, because of the low sensitivity and PPV of skin and specific IgE tests.