Calculation of plasma fibrin fiber mass-length ratios utilizing platelet aggregometers

We report a technique for measuring plasma gel fiber size utilizing optical platelet aggregometers. Three aggregometers were used to measure gelation kinetics and final gel turbidity: Sienco Model DP247E, Bio-Data Model PAP-2A, and Chrono-log Model 500-VS aggregometer. Each aggregometer was calibrated using dilutions of latex microspheres. Optical densities of microsphere solutions were measured at 626, 670 and 945 nm. Calibration curves were plots of aggregometer readings versus absorbance. Gels of various fiber size were prepared by varying thrombin concentrations and ionic strength. Fiber mass-length ratios were calculated from the wavelength dependence of gel turbidity. Gel optical densities at 640 nm and 945 nm were shown to be linear functions of fiber mass-length ratio. Aggregometer study gels were formed directly in aggregometer cuvettes. Gel formation kinetics were easily measured in the Sienco and Chrono-log instruments. Gelation kinetics in the Bio-Data instrument did not allow measurement of maximum turbidity. The latter value could be measured, however, once gelation was complete. Final aggregometer readings were made one hour after thrombin addition, and were converted to absorbance values using calibration curves. Absorbencies were then converted to mass-length ratios using the optical density versus mass-length ratio plots. Fiber mass-length ratios measured with aggregometers were in good agreement with those measured spectrophotometrically. This technique may allow routine quantification of plasma clot structure utilizing equipment ordinarily available in clinical laboratories.