New method for measuring ICG Rmax with a clearance meter.

The maximal removal rate of indocyanine green (ICG Rmax) is considered to be an important parameter of hepatic function. However, the method of analysis has some flaws, and an abnormal value is obtained for about 15% of patients. We developed a new method of measuring the ICG Rmax with a clearance meter (RK-1000) that continuously measured the ICG concentration using a fingertip optical sensor. Twenty patients were examined. The histologic diagnosis was as follows: normal for 10, cirrhosis in 6, hepatitis in 4. The ICG concentration was measured in vivo continuously with the RK-1000. To obtain the Rmax by the Michaelis-Menten model, the ICG concentration in the VLDL compartment was subtracted from the values obtained by the RK-1000 because ICG binds to various serum proteins and its rate of removal in the VLDL compartment differs from that in other protein compartments. The removal velocity was calculated and a Michaelis plot obtained. Then Rmax was calculated from the reciprocal of the y-intercept of a Lineweaver-Burk plot. The Rmax in subjects with liver disease was significantly lower than in those with normal liver. It is concluded that our new method of measuring ICG Rmax with the RK-1000 reflects liver function appropriately.