Quantitative correlations among fibrinogen concentration, sedimentation rate and electrical impedance of blood

Blood cells from 8 normal subjects, anticoagulated with EDTA, were washed twice with saline solution (100 mmol/l) and resuspended into saline solutions of different concentrations of human plasma fibrinogen. The erythrocyte sedimentation rates (ESRs) of these suspensions were determined by the Westergren method, and their resistance Rp and capacitance Cm were determined by measuring the impedances at three frequencies 100 kHz, 800 kHz and 1.2 MHz. The results showed that the logarithm of the ESR was proportional to the concentration of fibrinogen, Fb (g/l), expressed as: ln(ESR) = 0.468Fb - 0.10, (r = 0.96); and the haematocrit-normalised resistance R'p and capacitance C'm were both directly proportional to the concentration of fibrinogen, R'p = 3.99Fb + 465.0, (r = 0.87), and C'm = 49.7Fb + 628.2, (r = 0.96). The influence of fibrinogen on the impedance might partly be the result of interfacial polarisation and/or of red cell rouleaux formation. The results are useful for understanding the mechanism of the association between the impedance and the ESR of blood, and for finding means of improving the accuracy when estimating the ESR by the electrical impedance method.