Circadian variation of skin reactivity and allergy skin tests

Abstract

Previous investigations of the circadian variation in skin reactivity suggested that results of skin tests obtained in the afternoon could vary from the result: obtained in the early morning and therefore could result in a differing assessment of patient sensitivity. To determine whether this was a practical concern in the normal clinical setting, we studied 20 adults and 20 children who had skin prick tests positive (3 + or more) to short ragweed. These patients were skin tested in duplicate at 8 AM and at 4 PM with fivefold serial dilutions of short ragweed extracts (1:20 to 1:12,500, wt/vol) and of histamine hydrochloride (10 to 0.016 mg/ml). Areas of wheal and fare were recorded and measured by computed planimetry. In addition, results were also read according to a conventional scoring system. Mean wheal and erythema areas with ragweed and histamine at each dilution were compared between morning and their corresponding evening values. Although there was a trend for the morning means to be larger than evening means, no significant differences between the two sessions were observed at any dilution. Mean morning skin index scores, as calculated tom the combined mean wheal and erythema areas, were larger than mean evening scores for ragweed and histamine, but the differences were not of a degree to be clinically important. This observation was also true for conventional scores. Comparing the results from the two groups of children who had their first set of skin tests performed either in the morning or afternoon session indicated that there was no evidence of a refractory state of the skin during the second test sessions. We conclude that circadian variation of skin reactivity within the customary, clinic hours is minimal and should not affect the clinical interpretation of skin tests whether performed in the morning or the afternoon.