Electrical impedance and erythrocyte sedimentation rate (ESR) of blood.

The electrical impedance of blood is primarily determined by plasma resistance Rp, cell interior resistance Ri, and cell membrane capacitance Cm. These impedance parameters were measured for 62 samples with various erythrocyte sedimentation rates (ESR = 1-150 mm/h). A formula for estimating ESR by Rp and Cm was obtained by linear regression as: In (ESR) = 10.16-0.016 x f0, (r = 0.974, P < 0.001), where f0 = 10(9)/(2 pi.Rp100.Cm100) defined as the effective characteristic frequency in kHz, Rp100 = Rp/h in omega cm, Cm100 = Cm/h in pF/cm, h is the haematocrit in decimal. The 95% confidence intervals for the coefficients in the above equation were 9.73 to 10.59 and -0.017 to -0.015. The origin of the association was found reasonable since factors increasing the ESR, i.e., the concentration of some plasma proteins and the size of the blood cells, also elevate the capacitance. The results imply that the impedance measurement might be an alternative method for fast determination of the ESR.