Improved methodology for the evaluation of the velocity of clearance of indocyanine green in the rat.

Velocity of clearance of indocyanine green (ICG) is used for the measurement of liver function. Thirty-nine curves of ICG concentration vs. time, from 24 rats, were evaluated for the best method for the determination of the initial velocity of clearance of ICG. A bolus dose of ICG (0.66 +/- 0.10 mg/kg) was given, and [ICG] was recorded once per second for the 270 seconds from 30 seconds to 5 minutes after ICG administration with the aid of computer-assisted data acquisition. The 39 observed curves were then fit to six equations: a second- and third-order polynomial, the mathematical constant e raised to a first- (first-order kinetics), second-, and third-order polynomial, and an integrated form of the Michaelis-Menten equation. The residual errors of the fitted equation to the observed data were evaluated. First-order kinetics and an integrated form of the Michaelis-Menten equation were the least accurate methods of describing the [ICG]-time curve. The curve was better described by three equations: a third-order polynomial, e raised to a second-order polynomial, and e raised to a third-order polynomial. We recommend that one of the latter three equations be used in the determination of the initial velocity of clearance of ICG.