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Clinical & Experimental Allergy

Precise area determination of skin-prick tests: validation of a scanning device and software for a personal computer

Authors

  • L. K. POULSEN,

    Corresponding author
    1. Laboratory of Medical Allergology, National University Hospital, Copenhagen, Denmarl.
    2. Biotechnological Research Centre for Signal Peptides. National University Hospital, Copenhagen, Denmark
      Dr L. K. Poulsen, Laboratory of Madical Allergology, Medical Department TTA 7542. National University Hospital. 20 Tagensvej, DK-2200 Copenhagen N. Denmark.
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  • C. LIISBERG,

    1. Department of Optics and Fluid Dynamics, Risø National Laboratory, Roxkilde. Denmark
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  • C. BINDSLEV-JENSEN,

    1. Laboratory of Medical Allergology, National University Hospital, Copenhagen, Denmarl.
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  • H.-J. MALLING

    1. Laboratory of Medical Allergology, National University Hospital, Copenhagen, Denmarl.
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Dr L. K. Poulsen, Laboratory of Madical Allergology, Medical Department TTA 7542. National University Hospital. 20 Tagensvej, DK-2200 Copenhagen N. Denmark.

Summary

When skin-prick tests (SPTs) are used quantitatively, the circumference of the weal and/ or the flare is outlined using a felt tip pen, and transferred to paper by adhesive tape. The aim of the study was to develop and validate a procedure, objectively and precisely determining these areas after transfer to paper. A system was developed enabling the drawing of the area of weal or flare to be read by a hand-held scanner and calculated on a personal computer. Areas in the 5-500 mm2 range could be determined with day-to-day and interoperator coefficients of variation (CVs) of 3.3% and 1.1%, respectively. Accuracy was determined in two ways: by correlation to cutting/weighing of four times enlarged SPT areas (r2= 0.0, P< 0.0) and by measuring standardized areas (deviations less than intra-assay CV, i.e. 1-2%). For comparison, CVs of alternative methods were also determined: eight different areas (9-76 mm2) were evaluated in quadruplicate using the SPT-scanner (CV=1.1%), by cutting/weighing of paper (CV = 2.2%), by digitizing (CV = 4.4%) or by measuring longest and orthogonal diameters (CV= 13.13%). In conclusion, the scanning device and software provides an objective and reproducible procedure for rapid determination of SPT areas. When areas are determined by scanning, digitizing or cutting/weighing the variations in area determination becomes negligible compared to the variations of the entire skin test procedure.

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