Developing and testing of a screening tool to predict people without IgE-mediated allergy: a quantitative analysis of the predictive value of a screening tool

Victoria S Hammersley, Jessica Harris, Aziz Sheikh, Emma Davidson, Samantha Walker

Consultations in primary care for allergies are common. It can be difficult to differentiate between IgE-mediated (atopic) symptoms - which respond to allergen-specific interventions - and those that are non-atopic, without performing objective tests that are largely unavailable in UK general practice. To develop and test a screening tool that can accurately discriminate between atopic and non-atopic individuals. A validation study that took place in 2012 in adult volunteers aged >16 years in Scotland. A questionnaire screening tool was developed using questions from a large cohort study and through consultation with experts. Participants answered the questions and had skin prick tests for four aeroallergens (house dust mite, cat, dog, and mixed grasses). Participants were classified as atopic if any average wheal diameter was ≥3 mm bigger than the negative control. Sensitivity, specificity, and positive and negative predictive values of individual and combinations of questions were calculated. In all, 143 participants completed the questionnaire and underwent skin prick testing. Of these, 81 (56.6%) were atopic. Negative predictive values for the individual questions ranged from 48.2% (55 not atopic out of 114 negative answers) to 72.0% (18/25). An optimum combination of four questions was identified, in which a negative answer to all four questions was reported by 24 participants, 21 (87.5%) of whom were not atopic. The authors have identified a set of questions that correctly predict negative skin prick tests to common aeroallergens 88% of the time. These may be useful to exclude patients who do not warrant further investigation and who can reliably be advised that allergen avoidance is neither necessary nor helpful.