Plasma fluorescein decay determination during fluorophotometry.

Two useful methods for determination of the decay curve of non-protein bound fluorescein (NPBF) in plasma up to 1 hour after intravenous fluorescein injection are described and evaluated. The course of NPBF is approximated in method 1 by a sum of two exponential decay functions and in method 2 by a power of time function. The parameters in these functions are calculated with the use of concentration values measured in two blood samples taken at about 5 min. and 60 min. after injection. Calculations in method 1 include the amount of fluorescein injected. The accuracy of each method was evaluated in 7 volunteers by measuring NPBF concentration in 15-28 blood samples taken after fluorescein injection at intervals of 5 min. or less. The mean relative deviation between calculated and measured concentration values amounted to 9.2% +/- 4.3 SD and 12.7% +/- 4.5 SD for method 1 and 2, respectively. The time integral of NPBF concentration in plasma up to one hour after injection was calculated according to the results of both methods and compared with integral values obtained by linear interpolation between concentration values measured in the 15-28 plasma samples. The mean relative deviation for the 7 volunteers amounted at 15 min. to 2.8% and 17% and at 60 min. to 11% and 18% for method 1 and 2, respectively. The maximal difference between the blood-retinal barrier permeability value for NPBF calculated with and without taking glucuronation into account was estimated to be 20% for an average glucuronation percentage of 70% or less.