Comparison Between Colorimetric and Subjective Evaluation of Intradermally Injected Histamine-Induced Erythema in Healthy Dogs.

Colorimetric erythema measurement before and after intradermal injection can objectively replace subjective erythema scoring in canine IDT.

This study evaluated whether objective colorimetric measurement of erythema could replace subjective erythema scoring in the calculation of global wheal scores (GWSs) during intradermal testing (IDT) in dogs. Seven clinically healthy dogs received duplicate intradermal injections of a negative control and three histamine concentrations (0.0001%, 0.001%, and 0.01%) on the lateral thorax. Erythema was measured colorimetrically before and 15 minutes post-injection, and three blinded investigators simultaneously scored erythema subjectively as absent, weak, or strong. Among four colorimetric measurement approaches tested, subtracting the pre-injection colorimetric erythema value from the first post-injection value (ΔEfirst) performed best. This method produced GWSs with differentiation efficacy among the four solutions comparable to GWSs derived from subjective erythema evaluation. Notably, subjective erythema scores correlated more strongly with wheal diameter than did colorimetric measurements, suggesting a potential bias whereby investigators may unconsciously allow wheal size to influence their subjective erythema assessment. The authors conclude that a single pre- and post-injection colorimetric measurement, with calculation of the difference, can objectively replace subjective erythema evaluation in IDT interpretation. This approach may reduce evaluator bias and improve standardization of intradermal allergen testing in clinical and research settings. The study is limited by its small sample size (seven dogs) and the use of histamine rather than allergen extracts.

This summary was distilled by AI and may occasionally misinterpret data. Confirm critical details with the primary literature before clinical application.