Patch tests with potassium dichromate removed after 24 and 48 hours.

The rate of release in vitro of four potassium dichromate concentrations (0.5, 0.1, 0.05 and 0.01%) was determined. In the course of 24 h, 90.1-97.5% was released of the total K2Cr2O7 amount in 48 h. Out of 30 patients positive to 0.05% dichromate when the patch test was done routinely, 29 were also positive when the patch was removed after 24 h. The effect of the earlier removal of the patch test was also noted in seven other patients, when results of tests with lower dichromate concentrations were taken into account.