The longest wheal diameter is the optimal measurement for the evaluation of skin prick tests.
BACKGROUND
Mean diameter or longest diameter are the 2 most frequently used parameters for wheal response assessment after skin prick testing (SPT). We aimed to compare these 2 parameters taking as gold standard the surface of the wheal skin response.


METHODS
Patients suspected of having an allergic reaction against inhalant allergens have been skin prick tested using the Pan-European GA(2)LEN SPT panel. Fifteen minutes later, macroscopically evident wheal and flare reactions were marked with a pen and transferred to paper with a transparent scotch tape. Each paper-transferred wheal was scanned with an ordinary scanner, and its surface-corresponding maximum perpendicular diameters and longest diameters were measured using a computer software application for image recognition, developed for this purpose. Correlation coefficients (Spearman's rho) between surfaces and respective mean (rho(mean)) or longest (rho(longest)) diameters were calculated and subsequently compared.


RESULTS
1,554 SPTs were performed in 74 patients. In 264, a macroscopically evident wheal and flare response was observed. Both mean and longest diameters correlated significantly with the wheal surfaces. However, rho(longest) was statistically significantly larger than rho(mean) when the surface of the wheal was >17 mm(2) (rho(longest) > 0.860 vs. rho(mean) < 0.660; p < 0.05).Such a surface corresponds to a maximum diameter of approximately 7 mm and a mean diameter of approximately 6 mm. Thus, the larger the surface of the wheal, the more appropriate the usage of the longest diameter.


CONCLUSIONS
The longest wheal diameter alone seems to be a better surrogate marker of the wheal surface in comparison with the mean diameter. In addition, it is easier and faster to measure. Therefore, we propose this as the optimal methodology to evaluate SPTs.
Konstantinou
George N
GN
Department of Allergy and Allergy Research Center, Pediatric Hospital "P&A Kiriakou", National and Kapodistrian University of Athens, Athens, Greece. gnkonstantinou@gmail.com
Bousquet
Philippe-Jean
PJ
Zuberbier
Torsten
T
Papadopoulos
Nikolaos G
NG
D000485:Allergens / Q000008:administration & dosage / Q000276:immunology*; D057205:Automation, Laboratory; D005189:False Positive Reactions; D006801:Humans; D006967:Hypersensitivity / Q000175:diagnosis* / Q000276:immunology / Q000503:physiopathology; D007091:Image Processing, Computer-Assisted; D012867:Skin / Q000276:immunology / Q000473:pathology; D012882:Skin Tests / Q000379:methods* / Q000592:standards; D012984:Software; D014581:Urticaria
D000485:Allergens