Skin response to histamine dry skin prick test: Influence of duration of the skin prick on clinical parameters and on skin blood flow monitoring

Abstract

This comparative trial (histamine dry skin prick test versus control prick test) evaluates with subjective and objective clinical methods (i.e. itch scores, wheal area, and wheal and flare area) and with laser Doppler flowmetry (multiple sites measured between 5 and 15 min after prick test) the effect of increasing the duration of the skin prick (1, 3 and 10 s). As compared with control prick tests, all objective clinical parameters after histamine prick test were significantly different from the control prick tests. There was no interaction between agonist-duration of prick test and clinical parameters. When present, itch was reported only after histamine prick test. Skin blood perfusion values were evaluated with Laser Doppler flowmetry at prick test sites and at 1 cm distance from the prick test site. At control and histamine prick test sites, increased blood flow values were observed and a moderate interaction between agonist-duration of prick test and repeated measurement was noted (one tail P < 0.05); there were indeed lower values 9 min after histamine prick tests whatever the duration of the prick test. At 1 cm distance from histamine prick test sites, all skin perfusion measurements (either 5–8 or 11–14 min) showed increased values over data recorded after control prick test ( P < 0.0001). On pooled data recorded at distance from histamine or control prick tests, there was a significant interaction between agonist-duration of prick test and laser Doppler flowmetry ( P < 0.0004). Indeed, only moderate changes were recorded at distance from the control prick test, with the exception of the reaction induced by the 10 s control prick duration, where highly significant increases of blood flow were recorded 11–14 min after testing. This reflects activation of the axon reflex mediated vasodilation only after prolonged duration of the control prick. Laser Doppler flowmetry appears to be a reliable and highly sensitive method for objective quantitative measure of skin blood perfusion at sites of and at distance from histamine injection with the dry skin prick test; short duration (i.e. 1 s) is recommended in order to record specific histamine related signals in a repeatable way.