Think Twice before Interpreting the Skin Prick Test as Age, Body Mass Index, and Atopy Affect Reaction Time and Size

Introduction: The skin prick test (SPT) is a reliable method to confirm sensitization in IgE-mediated allergic diseases; however, it has been reported to be affected by several personal and environmental factors. Our objective was to determine the factors affecting the skin reactivity to histamine and allergens and investigate whether it differs according to age in terms of reading time. Methods: A total of 500 patients, aged 4 months–18 years, were enrolled in the study. Wheal and flare reaction sizes were documented as the mean of the longest and the midpoint perpendicular diameter in the 5th, 10th, 15th, and 20th min. Skin reactivity was compared between children >24 and ≤24 months of age. Results: We found larger histamine and allergen wheal sizes in children >24 months than the ones ≤24 months of age (p < 0.001 and p = 0.007, respectively). The duration of maximum histamine reactivity was 15 min for children >24 months whereas 10 min for children ≤24 months of age. The number of children losing their histamine reactivity after 15 and 20 min was significantly higher in the smaller age-group. Multiple regression analysis revealed a larger histamine reactivity in children >24 months of age, having obesity, and having allergen sensitization (p = 0.002, p = 0.003, and p = 0.018, respectively). Conclusion: It seems more accurate to evaluate SPT after 10 min in children ≤24 months of age. Cutoff values and ideal measurement time according to individual factors such as age, body mass index, or atopy are needed.