Optical analysis of red blood cell sediment formation

The red blood cell (RBC) sediment formation was studied using an optical method. The intensity of light transmitted through the blood sample was measured as a function of time and distance from the bottom of the sample. Blood was obtained from healthy donors and measurements were performed at initial hematocrits ranging from 30 to 50%. Sedimentation curves and time dependence of the intensity averaged along the height of the RBC suspension were determined to give a cumulative description of the process. Detailed analysis of the transmitted light intensity revealed a moving interface between sedimenting RBC aggregates and the forming of a deposit of the cells. It was shown that although there is no discontinuity in the intensity an averaged interface can be found. A novel curve describing the sedimentation process called the deposit formation curve was found. Below this curve a formation of the RBC deposit occurs. Firstly, this curve represents the position of the interface between sedimenting RBC aggregates and a forming deposit, secondly this curve coincides with the last part of the sedimentation curve.