Studies on the pathogenesis of the constitutional excretory defect of indocyanine green

Constitutional excretory defect of indocyanine green (ICG) is characterized by the selective impairment of plasma ICG clearance. We studied binding patterns of ICG to plasma proteins and plasma ICG kinetics in three patients and one relative. Binding patterns of ICG to plasma proteins were modified in subjects with the ICG excretory defect. However, plasma disappearance rates of ICG bound to various protein fractions were not significantly different from each other, except for one case. In the kinetic study of ICG hepatic uptake rates (a values) were decreased, and hepatic reflux rates (b values) were increased in ICG excretory defect and liver cirrhosis. However, a values were unchanged and b values were clearly increased in ICG excretory defect, while a values decreased and changes in b values were slight in liver cirrhosis after loading with a large dose of ICG. These results suggest that active transport of ICG in the hepatic cell membrane is selectively lost in the ICG excretory defect.