Patch test responses evaluated by cutaneous blood flow measurements.

We measured the cutaneous blood flow in positive standard patch test reactions by use of the laser-Doppler technique. The results were compared with conventional visual readings to develop a quantitative method. Compared with the basal blood flow in negative or nontested sites, the blood flow was significantly increased about fivefold in the doubtful reactions (?+), and about tenfold in both weak (1+) and strong (2+) positive reactions. The blood flows in the 1+ and 2+ reactions did not differ significantly from each other. No 3+ positive reactions were measured. We conclude that this method might be used to separate negative, doubtful, and positive reactions, whereas weak and strong positive reactions have to be differentiated by other means.