Optimization of skin testing

I. Choosing allergen concentrations and cutoff values by factorial design


Dr J. G. R. de Monchy, Department of Allergology, University Hospital Groningen, P.O. Box 30.001, 9700 RB Groningen, The Netherlands


Standardized extracts of Phleum pratensis (grass) and Dermatophagoides pteronyssinus (house-dust mite) were used as test allergens for multiple regression in order to determine optimum concentrations and cutoff values with regard to diagnostic capacity and safety. If a RAST value of class 1 or more was taken as an indication of sensitization, it was found that the optimum concentrations for the detection of sensitization are in the range 10–100 BU/ml and 1500–10000 BU/ml for intracutaneous tests (ICT) and skin prick tests (SPT), respectively. The skin test results were expressed as histamine ratios. Using allergen concentrations of 30 and 3000 BU/ml, we found cutoff values of 0.87 and 0.53 and predictive values of 87.1% and 19.1% for ICT and SPT, respectively. The maximum wheal size (mean wheal size + 2 SD) to be expected in 95% of the population was 26.6 mm (ICT) and 10.9 mm (SPT), sizes regarded as safe by most clinicians. In conclusion, by using this method with a limited number of patients, one can probably improve the diagnostic precision and safety of the skin test. In the second part of this study, these hypotheses were prospectively tested in a multicenter study.