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These reviews were published in the Journal of Clinical Pathology and a supporting series of cases in the British Medical Journal. See Authors and acknowledgments.

We recommend allergen specific IgE measurement in the presence of clinical suspicion of type 1 IgE mediated hypersensitivity/allergy, principally for inhaled antigens. There is no need to request total IgE when requesting RAST.

There is limited consensus guidance on use of RAST testing in particular, as distinct from allergy testing in general, and the guidance above is drawn principally from review articles and by extrapolation from clinical studies.

RAST refers to one of the first tests used to test allergen specific IgE, which is no longer in use; a more appropriate name is allergen specific IgE testing. It is used as a more accessible or more convenient alternative to skin prick testing [RCP and Royal College of Pathologists, 1994]. It is only useful for assessing type I IgE mediated reactions (immediate hypersensitivity); RAST tests are therefore not useful for assessing pseudo-allergic reactions that are not mediated by IgE (such as non-allergic food intolerance; reactions to radiocontrast media, morphine, aspirin; physical urticarias, etc.) [WHO, 1981; Kay and Lessof, 1992; RCP, 2003]. Angio-oedema without urticaria is usually not an IgE mediated allergic reaction [American College of Allergy and Immunology Board of Regents, 1991]. RAST testing and skin prick testing are of little value in chronic urticaria, which is usually not caused by IgE dependent mechanisms.

RAST tests must be requested for a specified antigen based on clinical history [WHO, 1981; American College of Allergy and Immunology Board of Regents, 1991; Kay and Lessof, 1992; RCP, 2003]. They are of no benefit as screening tests without specified antigens [American College of Allergy and Immunology Board of Regents, 1991; Kay and Lessof, 1992; RCP, 2003]. It follows from this that requests should not be for widespread antigen screening. Test results must be interpreted in conjunction with clinical findings [WHO, 1981; American College of Allergy and Immunology Board of Regents, 1991; Kay and Lessof, 1992; Sicherer, 1999; RCP, 2003].

The specificity and sensitivity of RAST results vary for different allergens tested (for example, poor for fruits and vegetables). Overall, RAST tests have relatively low sensitivity and can be negative in the presence of allergy [Saarinen et al, 1982; RCP and Royal College of Pathologists, 1994; National Asthma Education and Prevention Program, 1997; Li, 2002; Volcheck, 2001]. In addition, adverse reactions to foods are IgE mediated allergies in only about a third of patients [WHO, 1981; National Asthma Education and Prevention Program, 1997; Volcheck, 2001]. Therefore, RAST tests are of limited value in this situation. It follows from this that RAST testing in food intolerance is unlikely to be helpful, and we recommend that it used only in the initial investigation of severe acute food intolerance reactions where a specific food is suspected.

The efficacy of unconventional/alternative allergy testing has not been confirmed, and can neither substitute or complement RAST and other classic allergy tests [Kay and Lessof, 1992; RCP, 2003]. Therefore, these tests are not recommended.