Contributions of suspending medium to electrical impedance of blood.

Blood cells from ten normal subjects, anticoagulated with dried sodium heparin, were washed twice with phosphate-buffered saline (PBS) and resuspended with autologous plasma, serum, serum plus sodium heparin, and PBS. The resistance Rp and capacitance Cm of these suspensions were determined by measuring the impedances at three frequencies 100 kHz, 800 kHz and 1.2 MHz, and found to be dependent on the proteins and electrolytes of the suspending medium. Two suspensions with the same medium resistivity might have different resistances if the contents of the two mediums are different. The fibrinogen, serum proteins, sodium heparin and membrane contributed to Cm by 20%, 14%, 2% and 64%, respectively. For the samples with buffered sodium citrate as anticoagulant and in the haematocrit range 30-60%, the group washed and resuspended with PBS had a consistently decreased Rp and Cm compared to the original group. Sodium heparin seemed to be the best anticoagulant when studying the electrical impedance of blood. The influence of suspending medium might result in part from the altered interfacial polarisation. The results might be useful for understanding the origin of the impedance of blood, and imply that impedance measurement may be an alternative method for screening purposes for diseases that involve abnormal compositions of certain plasma proteins.