Skin prick test and specific serum IgE in the diagnostic evaluation of suspected cow's milk and hen's egg allergy in children: does one replace the other?

Background The measurement of specific serum immunoglobulin E (sIgE) and the skin prick test (SPT) are accepted tools in the diagnostic work-up of suspected food allergy. Often only one of the methods is used to determine sensitization; however, it is still under debate whether these two methods can be used interchangeably. Objectives To investigate the concordance of SPT and sIgE serum assays with regard to suspected food allergy. Methods In 395 children referred to our clinic with suspected cow's milk allergy and in 268 children with suspected hen's egg allergy specific immunoglobulin E (IgE) was measured, a SPT and an oral food challenge performed. A weal size >= 3 mm and sIgE >= 0.35 kU/L were considered positive. The weal size of the SPT and the level of food-specific IgE were tested for correlation for each allergen. Results Of the 395 (23%) children orally challenged with cow's milk, 92 showed no corresponding results for SPT and sIgE as either positive or negative. For hen's egg, in 27 of 268 (10%) children differing test results for SPT and sIgE in serum were obtained. Moreover, regarding the quantitative values for sIgE and SPT in children with or without clinically relevant food allergy, sIgE and SPT correlated badly. Conclusions The concordance between SPT and sIgE is surprisingly low for cow's milk and hen's egg on an individual basis. Therefore, the tests should not be used interchangeably. Especially in children who receive a negative test result the alternative test should also be used. Furthermore, our data indicate again that oral food challenges are still the method of choice to diagnose food allergies.