Effect of glycerin on immediate cutaneous reactions of histamine (positive) and phosphate-buffered saline (negative) controls in intradermal skin testing of healthy dogs: A randomised, blinded study.

Abstract

Glycerinated allergen extracts contain 50% glycerin, an excellent preservative. While glycerin is a recognised irritant in humans, the utility of glycerinated extracts for intradermal testing has not been validated in dogs. To determine and compare the effects of glycerin on immediate cutaneous reactions to intradermal injections of histamine and saline in healthy dogs. Eight healthy laboratory beagles. The study was designed as a randomised, blinded study. Intradermal injections of histamine (positive control) and saline (negative control) in aqueous and glycerinated (50%) forms were performed on the right thorax. Global wheal scores (GWS) at 20 min were evaluated by two independent investigators blinded to the interventions. There were no wheal and flare reactions observed after the intradermal injections of phenolated saline. By contrast, 50% glycerosaline injections induced erythema and induration in all dogs. Global wheal scores were significantly higher in aqueous histamine (Friedman test, p< 0.0001) and 50% glycerinated histamine (Friedman test, p= 0.0084) compared to phenolated saline controls. Interestingly, only aqueous histamine (Friedman test, p= 0.01) had significantly higher GWS than 50% glycerosaline injections, while no significant difference in GWS between 50% glycerinated histamine and 50% glycerosaline groups was observed (Friedman test, p= 0.59). This study demonstrates that intradermal injection of 50% glycerosaline induces erythema and induration skin reactions in healthy dogs that can mimic positive reactions to allergenic extracts. Further dilutions of glycerinated positive and negative control solutions need to be optimised for intradermal testing in dogs.