Multiple concomitant positive patch test reactions

Thirty-five patients who showed 90 one plus (+) patch test reactions to 28 patch test chemicals at Day 2 (D2) were retested to the chemicals at D7. On retesting, 60 % (54/90) reactions were positive but 42 % (38/90) were negative at D9, suggesting that false positive patch test reactions were common when more than one positive reaction was obtained by concomitant patch testing. On retesting, the total % positivity was reduced from 344 to 241 suggesting that the true index of sensitivity was falsely exaggerated by concomitant testing.