Implications of the dielectrical behaviour of human blood for continuous online measurement of haematocrit.

A study was designed to explore the possibility of detecting the haematocrit of blood by means of admittance measurements. The admittance and phase angle of blood kept in a measuring cell were determined at various frequencies between 60 kHz and 24 MHz. A reliable and accurate estimation of haematocrit was obtained in two ways. First, low-frequency admittance, high-frequency admittance and a factor x, which was the conductive percentage of cell content, were used. Secondly, the maximum phase angle was used. Both methods can be applied to obtain continuous on-line information about haematocrit for blood volume control during haemodialysis.