Automated measurement of skin prick tests: an advance towards exact calculation of wheal size.

BACKGROUND

Using the Khoros image processing software environment, we developed a software-based system capable of extracting wheal size from skin prick tests (SPTs) in mm(2) for research and routine purposes.

METHODS

At 20 min, the outlines of up to 20 wheals were marked with a pen and transferred with translucent adhesive tapes to a white paper form carrying predefined markings. The form was scanned at 200 dpi. The software automatically analysed the scanned image and calculated the sizes of the wheals. In a pilot study, serial SPTs with histamine in increasing dilutions were performed in 12 healthy volunteers in duplicate on both volar forearms. We matched the application results with a reference created from the scanned pictures.

RESULTS

Bland-Altman analysis showed reference and software calculation reaching very high agreement. The comparison of reference/software resulted in a low centred coefficient of variation (COV) of 11.9%. This was superior to the conventional measurement of horizontal (COV 37.9%) or maximal/minimal diameter (COV 25.9%).

CONCLUSION

We present an accurate tool for exactly calculating SPT wheal size in mm(2).