Six-Hour Versus 48-Hour Patch Testing With Varying Concentrations of Potassium Dichromate

This study examines the possibility of using patch contact times shorter in duration than the standard 48 hours. Using varying concentrations of potassium dichromate (K₂Cr₂O₇), this study analyzed results from two sets of patches applied to the backs of 11 subjects for durations of 6 and 48 hours, respectively. Results showed that after the 48-hour application period, all subjects reacted to K₂Cr₂O₇ at some concentration. For the patches applied for 6 hours, 7 of the 11 subjects (64%) reacted to K₂Cr₂O₇ at some concentration. Minimum elicitation thresholds (METs), the lowest concentration at which a reaction was observed, were established for both the 6-hour and 48-hour application times. The ratio of an individual's 6-hour MET to their 48-hour MET was calculated to evaluate the feasibility of patch testing with a higher concentration of an allergen for a shorter time period. Although the results clearly indicated that a higher concentration of allergen is required in order to elicit a reaction at 6 versus 48 hours, a fair amount of interindividual variability is exhibited by these 6-hour to 48-hour MET ratios. This observed variability would seem to preclude the use of 6-hour duration patch contact times for routine patch testing with K₂Cr₂O₇.