Diurnal Variations in Skin Prick Testing.

Background: Prior research suggests that skin prick testing (SPT) might be larger in the afternoon, with unclear clinical significance. Methods: 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). Results: 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. Conclusions: 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.