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The Specific IgE Blood Test (previously known as RAST) identifies the presence of allergy related (IgE) antibodies circulating in the blood stream. However, whilst allergy is unlikely when specific IgE antibodies are absent, their presence only indicates that sensitisation has occurred, it does not diagnose the allergy. For this reason, the allergy specialist has to take an allergy focused medical history in order to accurately diagnose the allergy. This is especially important in the case of suspected food allergy when an inaccurate diagnosis may commit the patient to lifelong, but unnecessary, food avoidance.
This is why allergy tests need to be interpreted by allergy specialists. It also explains why it is important not to test everybody for every known allergy without reference to an allergy-focused medical history, an approach that would inevitably lead to errors in diagnosis.
The ISAC ImmunoCAP Blood Test simultaneously measures antibodies to 112 important airborne, food and other allergens and can either be performed on a standard blood sample or even a fingertip blood sample taken at home and sent through the post.