Detection of antifood IgE by in vitro tests and diagnosis of food allergy.

The diagnosis of IgE-dependent food allergy relies on the demonstration of specific IgE by prick tests or biological tests. A radioimmunoassay (RAST Phadebas) is completed by several immuno-enzymatic methods: RAST Phadezym, FAST, MAST-CLA, AlaSTAT, etc. The allergen is bound to solid or liquid phases, by different binding agents. Various enzyme-substrate systems, and several systems for expression are used (RIA, fluorescence, chemoluminescence, colorimetry, etc.). Another aspect of modern technics is the trend towards high automated processes. A second group of tests aims to detect the release of mediators from sensitized basophils: leucocyte histamine release test, human basophil degranulation test and a leucocyte leukotriene release test. The specificity of tests for detection of anti-food IgE is lessened by numerous cross reactivities between pollens, fruit, and vegetable. The study of the sensitivity of such tests needs strictly standardized food challenge tests in order to firmly establish the diagnosis of food allergy. Multiscreen tests have to be assessed, in order to validate their efficacy for detecting frequency allergens. Whatever the test to be used, its positivity means only sensitization, and food challenge tests are mandatory to recognize true food allergy, as latent sensitization to food is a current phenomenon in atopic children. The possibility of reliable diagnosis of food allergy by using challenge tests makes now possible and advisable to set up quality controls for all biological tests applied to the detection of antifood IgE, thanks to the possibility to dispose of reference sera.