[Precision and economy of skin prick tests]

Due to a rise in the number of cases of allergic disease and a need to increase financial resources for the diagnosis of these conditions, the possibility of reducing costs of skin pricks tests (SPT) was very welcome. In an attempt to reduce costs some practitioners use one lancet for several pricks in one patient. The purpose of this study was to determine whether this way of performing SPT influences the results. 52 subjects with (39) and without (13) atopy were tested with histamine, codeine and standard allergen extracts. SPT were applied to the volar surface of a randomly assigned forearm using two methods: one lancet-one prick on one forearm (single test method) and one lancet-multiple pricks ("multiple test" method) on the other. The false positive tests at the placebo site following allergen were recorded only in multiple test method, in 41 out of 72 pricks (p < 0.00001) when all reactions above baseline were considered and in 26 out of 72 (p = 0.00001) when a 3 mm cut-off was considered. The size of the false positive reaction depends on the intensity of the reaction to the preceding allergen (rang Spearman factor R = 0.706, p < 0.000001) and decreases in the second consecutive placebo test. Our data show that one lancet for multiple test method cannot be used to diagnose factors responsible for allergy, particularly in patients qualified for immunotherapy and in scientific studies. For financial reasons multiple test method can be used in screening and epidemiological studies where atopy is studied and there is no need to identify the specific allergen.