Quantitative determination of skin reactivity by two semiautomatic devices for skin prick test area measurements

For quantitative use of skin prick tests (SPTs), the circumference of the wheal and/or the flare is outlined by a pen, and transferred to a paper by adhesive tape. The biological response is considered proportional to this area. We have previously developed software, the SPT-scanner, for determination of SPT areas (5-500 mm2) by a hand-held scanner and a personal computer. This study is aimed at comparing the SPT-scanner with another semiautomated system, where the outline of the wheal is followed by a digitizer pen. Comparing 2080 SPT areas from a pharmacological study of cetirizine, the two systems correlated well (r = 0.980, p < 0.001), the digitizer generally giving larger areas than the SPT-scanner. Probably, the line is considered as a part of the wheal/flare in the digitizing system, whereas the scanner only detects areas within the circumference. In conclusion, the SPT scanner is objective and reproducible for rapid SPT area determination.