Quantification of skin blood flow at patch test sites

Irritancy caused by the patch test procedure itself can be evaluated by measuring the skin blood flow with a laser Doppler flowmeter before application of the patches and at intervals after their removal. To investigate this technique further, van der Bend and True test patches with and without nickel sulfate were applied to the skin of the back and to the volar forearm in healthy subjects. Immediately after removal of the patches, the blood flow values in 26 of 32 test sites were higher than the corresponding pre-application values. In the majority of cases, blood flow had returned to pre-application values at 72 h (24 h after removal). This favours these patches compared to those used in previous studies (A1-test, Finn chambers, Silver patches), which caused a more lasting effect on skin blood flow. The common practice of relying mainly on the 72 h and 96 h readings of patch test sites was thus justified.