Use of Indocyanine Green (ICG) in Hepatology

Abstract

The organic anion indocyanine green (ICG) is eliminated solely via hepatobiliary excretion. Consequently, ICG is used to measure the hepatic blood flow by a constant intravenous infusion of ICG, with measurements of ICG blood concentrations in an artery and a hepatic vein, and calculation by Fick’s principle according to simple mass conservation. Secondly, ICG is used to estimate various hepatic clearances, using constant intravenous infusion or bolus injection of ICG and measurements of concentrations of ICG in peripheral blood. These clearance values reflect hepatic blood flow and hepatobiliary excretory function depending on hepatic removal kinetics and systemic blood circulation at the (patho)- physiological condition studied. Third, during recent years, a simple ICG 15-minute retention test (ICG-r15) is developed, using intravenous bolus injection of ICG, measurements of ICG concentration in peripheral blood after 15 minutes, and calculation of percentage ICG of the dose injected which is retained in the body. The ICG-r15 test, which is primarily used to assess the hepatobiliary excretory function but also a wide range of other conditions, is however based on dubious physiological assumptions. In this review, we go through these various applications of ICG measures in hepatology, focusing on physiological background of the tests and their use in studies of liver hemodynamics during normal conditions and liver diseases.