New optoelectronic device for real time monitoring of human blood sedimentation

We report on a new optoelectronic device for monitoring human blood sedimen tation and for the determination of the erythrocyte sedimentation rate (ESR ), based on spectroscopic contrast between plasma and sediment. The radiati on generated by a yellow light-emitting diode (LED) at 570 ran is transmitt ed through the plasma volume formed during the sedimentation process, while the sediment itself is practically opaque at this wavelength. The transmit ted light flux measured by a photodiode is proportional to the height of th e plasma column in the cell, so that complete time evolution of plasma heig ht can be obtained. The time derivative of these curves yields the sedimentation velocity that passes through a maximum. The device was tested using an aqueous suspension of red latex spheres. The ESR obtained for human blood correlates with tha t determined by the conventional Westergreen method, but anti-correlates wi th the haematocrit. Due to the reduced cell volume, the quantity of sample needed for analysis is 30 muL (instead of I mL); in addition, the time scal e of the process is reduced by a factor 4 in comparison with the Westergree n method.