Indocyanine green (ICG), a fluorescent dye, is solely excreted by the liver without enterohepatic recirculation. We have recently shown the feasibility of a noninvasive transcutaneous ICG clearance to assess hepatic function instantaneously.

In this follow-up study, 10 dogs with congenital extrahepatic single portosystemic shunt (PSS) were included. Before and 3 months after surgical closure with cellophane banding or silk ligature, a ICG clearance study was both done transcutaneously and fluorometrically by taking serial blood samples 0, 1, 3, 6, 9, 18, 42 and 64 min after IV injection of 0,2 mg/kg ICG. Transcutaneous ICG clearance was measured using 2 miniaturized devices to detect ICG fluorescence with an excitation wavelength of 760 nm and an emission wavelength of 820 nm. For both methods, half-life time (HLT_Se, HLT_tc), plasma disappearance rate (PDR_Se, PDR_tc) and 15 minutes retention rate (R15_Se, R15_tc) were calculated based on the curve within minutes 1 to 15 after ICG injection. PSS closure was defined based on Doppler sonography and angiography.

In 6/10 dogs, the shunt vessel was closed after 3 months. In 3/10 dogs, the PSS was still partially open. One dog died after the operation. Transcutaneous ICG clearance was easily performed without complications and was well tolerated by all dogs. There was a significant difference between open and closed PSS for PDR (PDR_Se: p=0.0095; PDR_tc: p<0.0001) and R15 (R15_Se: p=0.0323; R15_tc p<0.0001) but not for HLT. Linear correlation coefficient between PDR_Se/PDR_tc, R15_Se/R15_tk and HWZ_Se/HWZ_tk were R²=0.6169, R²=0.4629 and R²=0.08629, respectively. In contrast to the invasive method, there was no overlap except one dog of PDR_tc and R15_tc of open and closed PSS.

In this first transcutaneous ICG clearance study of dogs with liver disease, transcutaneous assessment was superior to the invasive method and results are available immediately. The very limited invasiveness of this method and its dynamic character make the transcutaneous liver function test with ICG clearance a worthy test for veterinary medicine.

Disclosures

One author (N. Gretz) is owner of a patent using transcutaneous measuring devices.