The Predictive Value of Specific IgE Levels for the first diagnosis of Cow's Milk Allergy
Pediatric Allergy and Immunology. July '07 [Epub ahead of print]
BY: Miceli Sopo S, Radzik D, Calvani M.
Department of Pediatrics, Catholic University of Rome, Rome, Italy
Cow's milk allergy (CMA) is a very common paediatric condition affecting between 2-7% of infants under three. It can manifest in a number of ways, such as: enteropathy, oesophagitis, atopic dermatitis and asthma. The gold standard diagnostic test is a direct, supervised food challenge (FC) but this can hold potential risks. Therefore a number of surrogate markers of allergy can be used to support a clinical diagnosis the most commonly used being skin prick testing and specific serum IgE to cow's milk proteins.
This review article from a group in Italy has set out to try and make sense of the conflicting data on specific IgE testing in CMA. In particular the authors have highlighted the discrepancies in cut-off levels of specific IgE between numerous studies in this field. In most screening tests where the goal is to have a high sensitivity and high negative predictive value (NPV) at the expense of a low positive predictive value (PPV). In this instance, the goal here is to protect 'at risk patients' from the gold standard test, a food challenge. Therefore studies have chosen cut off levels of specific IgE to CMA that are highly specific with a very strong PPV. However, as this paper shows, there is wide variation in levels of specific IgE CMA above which, it is not recommended to use a FC. The levels range from 3.5 kU/l to 88.8 kU/l, as the authors point out which of these is right. The paper also points out that these values are only valid if the test is performed using the Pharmacia CAP-system.
Although CMA is an increasing problem with considerable morbidity, elimination diets can be difficult and expensive. Therefore accurate diagnosis is always important. The authors conclude that with a few exceptions most infants with suspected CMA should have a FC. The exceptions are a history of anaphylaxis, which is obvious to most, and infants with atopic dermatitis, a history consistent with CMA and a specific IgE >50kU/l. CMA.