Cellular allergen stimulation test (CAST) 2003, a review.

Specific diagnosis of immediate type allergies, such as rhinoconjunctivis, asthma, urticaria/angioedema and anaphylaxis, particularly when IgE-mediated, traditionally rests on prick and/or intradermal skin tests and, since about 30 years, on the determination of allergen specific IgEs. Some cellular tests, i.e. tests determining the reactivity of blood cells in vitro, particularly basophils, to allergens, have been available for many years. The determination of histamine release has been widely used in allergy pathophysiological research but its routine application in allergy diagnosis has been restricted to few groups. Basophil degranulation, as determined by microscopic examination, was promoted by some groups in the 1980's but has been largely abandoned since around 10 years ago; an alternative cellular test, based on the determination of sulfidoleukotrienes (LTC4, LTD4, LTE4) produced by IL-3 primed basophils stimulated by allergens in vitro, has been proposed. This test became available commercially in 1993 under the name of CAST (Bühlmann Laboratories, Allschwil, Switzerland). The CAST assay has been used in allergy diagnosis in a variety of indications, such as inhalation allergies, allergies to insect venoms, foods, occupational allergens and various drugs. A large number of reports on CAST diagnostic value, however, have been anecdotal. A meta-analysis of validated and well controlled studies encompasses 37 studies, 1614 patients and 1145 controls. This should definitely establish the value of this diagnostic test, particularly in instances where other in vitro or in vivo diagnostic tests are not reliable, such as food or drug allergies, as well as in non-IgE-mediated immediate hypersensitivity reactions. However, a number of questions about the CAST diagnostic assay are still open or have not been systematically explored. This may explain, in addition to the practical limitations inherent to all allergy cellular tests, why CAST has not yet become a very widely used assay worldwide, having gained broad acceptance in some countries but not in others.