Validity and Repeatability Characteristics of a Non-Invasive, Infrared-Based Method Estimating Plasma Indocyanine Green Decay in Healthy Dogs

Abstract

Plasma clearance of indocyanine green (ICG-CL) is an invasive method to evaluate liver dysfunction. We aimed to investigate the practicality of a noninvasive, transcutaneous, infrared-based method estimating the disappearance rate of indocyanine green (ICG-PDR). In a randomized, cross-over study, both ICG-CL and ICG-PDR were determined in eight healthy dogs while conscious and when sedated with medetomidine and medetomidine–vatinoxan. ICG-PDR was further repeated in six of the dogs to assess its repeatability. Differences were tested with repeated-measures analysis of variance and post hoc t-tests with Bonferroni corrections, while associations were evaluated by both Spearman and Pearson correlation analyses. Furthermore, repeatability was assessed by examining calculated coefficients of variation (CV). A significant decrease in ICG-CL was observed in dogs sedated with medetomidine, while no difference between conscious and sedated states was detected with ICG-PDR. Overall, correlations between ICG-CL and ICG-PDR were poor, as was the intrasubject repeatability of ICG-PDR in conscious dogs with CV consistently above 20%. While some of the results may be explained by poor signal quality for the non-invasive method, we conclude that in healthy dogs ICG-PDR performed poorly.