Diagnosis and Immunotherapy of Mould Allergy

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Abstract
To determine reproducibility and the optimal way of expressing skin sensitivity, simultaneous skin prick tests (SPT) and intradermal tests (ICT) were performed on 25 mold-allergic patients. The patients had a well-documented history of allergy to Cladosporium and Alternaria, and were tested with partially purified standardized extracts of these 2 mold species. SPT were carried out on the volar side of the forearm and ICT on the backs of the patients. The skin tests were performed as titration using quadruplicate determinations of 10-fold allergen dilutions. The area of the skin reactions measured by planimetry were plotted in a log-log system as a function of the allergen concentration. The reproducibility (SD mean area .times. 100%) of the ICT was significantly higher than that of the SPT (17% vs. 29%). A very low reproducibility was found with wheal areas < 5 mm2. The dose response curve of the SPT wheal area was steeper than that obtained with ICT, both concerning ICT wheal and flare. Increasing the allergen concentration with a factor 10 resulted in a doubling of the wheal area in SPT, in contrast to a factor 1.7 using ICT. THe coefficient of correlation using linear regression on the dose response curve was always > 0.9 with SPT and ICT wheal, but significantly lower with ICT flare. Skin sensitivity was estimated as end-point and histamine equivalent reaction. No significant correlation between SPT and ICT end-point titration was found, contrary to the histamine equivalent reaction. The difference in allergen concentration between end-point and histamine equivalent reaction was a factor 500 (median) for both SPT and ICT. Due to the lower reproducibility of small skin reactions, the histamine equivalent reaction is to be preferred as an estimate of skin sensitivity. The simplicity and the steeper dose response curve of SPT outweigh the lower reproducibility compared with ICT, and with the use of potent allergen extracts. ICT has no advantages over SPT.

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