The basis of any diagnosis of allergy requires a good history and examination, which should then provide a certain degree of confidence as to whether or not allergy is present. However, the diagnosis cannot be confirmed on the basis of symptoms alone, because both allergic and non-allergic conditions can present with similar symptoms. Based on prevalence figures, about half of the patients presenting with allergic symptoms in primary care may be non-allergic. Therefore, allergy testing in the form of specific IgE (sIgE) measurement and/or skin prick testing is an invaluable aid in demonstrating both the presence and severity of such an allergy. The usefulness of such tests extends beyond just the positive or negative result. Often, more information can be gleaned by using the test results in a form of a continuous variable in order to determine the likelihood that allergy can be attributed as an explanation for patients' symptoms and disease. In this review, we describe the rationale for utilising specific IgE antibody tests in diagnosing allergy. Furthermore, to optimize the information gained from allergy testing, we describe how to employ one particular well-validated IgE testing system for determining the likelihood that an individual patient's disease can be attributed to allergy.