Real-time assessment of canine liver function: variation of transcutaneous determined indocyanine green plasma disappearance rate (icg-pdr) in healthy dogs

Indocyanine green (ICG) is a fluorescent dye exclusively eliminated by the liver into the bile. ICG clearance determination has been used successfully to evaluate hepatic function in laboratory dogs. However, it has rarely been used in clinical setting as the analysis of the serum ICG concentration requires an advanced laboratory technique (high performance liquid chromatography). Our recent study in healthy Beagle dogs revealed a good correlation (r²=0.81) between ICG clearance and a transcutaneous method determining the ICG plasma disappearance rate (ICG-PDR in %/min) with a near infrared spectroscopy probe placed on the tail.1 In human medicine, the main indication for measuring ICG-PDR has been the prognostic assessment of liver failure and liver transplantation. The present study evaluated the day-to-day variation of ICG-PDR in healthy Beagle dogs to assess the repeatability of the test.
We studied six healthy laboratory Beagle dogs undergoing ICG-PDR testing on three consecutive days, in standardized conditions. ICG was given intravenously (0.5 mg/kg) and ICG-PDR was determined by using the PulsioFlex monitoring platform with the LiMon module probe (Pulsion, Munich, Germany). Daily ICG-PDR values from all dogs were compared and the coefficient of intrasubject variation (%CV) was calculated. Mean ICG-PDR was 7.8 ± 3.4%/min on day one, 8.8 ± 3.7%/min on day two, and 7.9 ± 2.6%/min on day three. There was no significant difference between the days and the mean ICG-PDR was similar to previously reported data (7.79 ± 3.3%/min). However, the mean %CV of ICG-PDR was very high (35.9 ±16.8%) with the highest individual %CV being 52.5%. In this limited number of animals, repeatability of transcutaneous ICG-PDR in its current form was rather poor. It seems unlikely that the test method will be useful for the repeated assessment of mild to moderate changes in canine liver function. However, future studies are warranted to assess the prognostic value of ICG-PDR for canine patients with severe acute or chronic end stage liver failure comparable to its current indication in human medicine.