Effects of diluents on skin tests

The role of diluents and preservatives on skin tests was examined in 41 allergic patients. The effect of glycerol in intradermal tests was studied. Concentrations of five percent glycerol were shown to induce a significant wheal which was not inhibited by clemastine fumarate, suggesting a direct toxic effect without the participation of histamine release. Twenty five Dermatophagoides pteronyssinus allergic patients were prick tested with standardized and lyophilized extracts reconstituted either in saline, 50% glycerol or human serum albumin. The wheal size induced by saline or HSA diluted extracts was very similar but greater than that elicited by extract dissolved in 50% glycerol. The correlation between prick tests induced by the three types of extracts tested was always significant.