Estimation of red blood cell volume fraction from overall permittivity measurements

The rapid testing of red blood cell (RBC) volume fraction (“hematocrit”) is becoming increasingly important to identify blood disorders (“hemoglobinopathies”). Electromagnetic techniques provide an advantageous way to measure blood properties, primarily because they are inexpensive, quick and noninvasive. The goal of this paper is to develop estimates of the RBC volume fraction levels of whole blood from macroscopic electromagnetic (permittivity) measurements. The approach taken is to generate volume fraction estimates by inverting classical bounds on the effective permittivity of dielectric mixtures. The usefulness of the approach is that, given the permittivities of the plasma (known), cells (known) and whole mixture (measured), one can determine the cell volume fraction and compare it to the levels found in healthy blood. The deviation of the properties can be used to help characterize certain blood disorders. The expressions developed are not limited to RBC measurement, and are applicable to any cell-in-solution system. Through correlation of our laboratory measurements, the analytical expressions and direct large-scale numerical simulations, the results suggest that RBCs form high-permittivity cell-networks by making cell-to-cell contact, even at relatively low volume fraction.