Phadiatop compared to skin-prick test as a tool for diagnosing atopy in epidemiological studies in schoolchildren

The validity of the Phadiatop test as compared to the skin-prick test (SPT) for diagnosing atopy in the epidemiological field has not been studied in schoolchildren. The aim of the present study was to evaluate its validity for classifying schoolchildren 9-12 yr old into atopics and non-atopics. A total of 621 children whose parents authorized both a SPT and a blood extraction from all children participating in the phase II of the International Study of Allergies in Children (ISAAC) in Cartagena (Spain) were included in the analysis. A positive SPT was that with at least a wheal having a maximum diameter of 3 mm, once the negative value had been subtracted. Phadiatop was performed according to the manufacturer instructions. Diagnostic tests using SPT as the gold standard were calculated for the whole group of children and also for those with asthma or rhinoconjunctivitis and for children without any of them. The results of the tests were: sensitivity 85.0% (95% CI 82.2-87.8%), specificity 85.5% (95%CI 82.7-88.3%), positive predictive value 72.7% (95%CI 69.0-76.1%), negative predictive value 92.7% (95%CI 90.6-94.7%) and accuracy 85.3% (95%CI 82.3-88.0%). The results improved among the symptomatic groups. Phadiatop can be used as a valid alternative to SPT in the epidemiological setting to diagnose atopy.