Diurnal Variations in Skin Prick Testing

Prior research suggests that skin prick testing (SPT) might be larger in the afternoon, with unclear clinical significance. This retrospective chart review analyzed SPT results from patients between June 2008 and June 2017, organized into 4 time groups for analysis (Group 1: 7:00 AM -10:29 AM, Group 2: 10:30 AM -11:59 AM, Group 3: 12:00 PM -2:29 PM, and Group 4: 2:30 PM -8:15 PM). In total, 12,982 (n) patient test results had positive histamine and were included in final analysis. Histamine wheal size was not significantly increased in the PM compared with AM (P = 0.89). Food allergen and aeroallergen wheal sizes were not significantly increased in PM. Histamine erythema size was increased in the PM compared with AM (P ≤ 0.01). Food allergen and aeroallergen erythema sizes trended toward an increase in the PM. There were not significant differences in SPT wheal size based on time of day for histamine, food allergens, or aeroallergens. SPT can be reliably performed at any time of day.