We evaluated a new method of computer-based scanning of skin prick tes
t wheal areas. To test the calibration of the program, we scanned five
constructed circles of exactly defined areas between 5 and 255 mm(2).
One of these circles was scanned in different degrees of contrast (mo
des), the middle mode being used in the other experiments. We also inv
estigated the inter- and intraoperator variation, Finally, results obt
ained by measuring diameters of wheals and by the new method of area d
etermination were compared for 82 histamine and 75 egg wheals. The are
as found agreed well with the real areas (P<0.01) (mean 97.4-100.8%),
except for the smallest wheal (5 mm(2)) (NS). Areas obtained in the ''
middle position'' closely resembled the real area. The intraoperator c
oefficient of variation (c.v.) was 1.4% (0.3-4.3), the day-to-day c.v.
was 1.9% (0.2-5.3), and the interoperator c.v. was 2.3% (0.7-5.7), wi
th a higher c.v. for small areas. Histamine and egg wheals were signif
icantly larger with the diameter method (126% and 129%, respectively)
than with the area method. The difference between the methods was most
pronounced for small wheal areas. The c.v. of the scanning method was
significantly lower than that of the diameter method. The new program
is precise and is recommended for registration of skin test reactions
in scientific trials. Although the scanner works well and has high pr
ecision, the major problem in skin testing seems still to be the repro
ducibility of the skin test technique employed.