Simultaneous determination of hemolysis and hematocrit in extracorporeal circulation by plasma surface reflectance spectroscopy

To achieve quantitative non-invasive optical diagnosis of blood abnormalities during extracorporeal circulation therapies, plasma surface reflectance spectroscopy was developed by implementing oblique-incidence optical fiber reflectometry on the surface of circulating blood. The reflected light in the wavelength range from 450 to 600 nm changed with respect to the plasma free hemoglobin level and could be used to quantify the free hemoglobin at an accuracy of 5.7±3.5 mg/dL. In contrast, the spectrum did not changed by varying the hematocrit. In the wavelength range from 600 to 800 nm, the obtained spectrum was affected by both the hematocrit change and hemolysis. The linear correlation between the hematocrit value and the spectrum was confirmed at R² = 0.99. The feasibility of determining of the hematocrit of arbitrary hemolyzed blood was confirmed. The developed system permits the extraction of the optical characteristics of both plasma and red blood cells without centrifugation. The study establishes non-invasive optical diagnostics capable of analyzing the optical properties of both plasma and red blood cells.