Some of the most effective methods to separate circulating tumor cells (CTCs) from normal blood cells can be implemented using ultra-filtration, and/or electro-magnetic fields. As well known, each biological cell presents, on both sides of its membrane, different concentrations of ionic species that produce an electric charge concentration with respect to the lipid double layer (impermeable to ions). In this way, the bio-cell can be seen as an electric capacitor, which has the lipid double layer acting as an insulator inserted between two conductive plates, concentrated on the lipid double layer inner and outer surfaces. In this paper, firstly, the electrical capacitor equivalent system is used to treat different types of bio-cells normally flowing in blood vessels (red blood cells, lymphocytes and various types of CTCs-like), and to transform their biological characteristics into digital twin information useful for engineering applications. After, the preliminary 3D geometric analysis of the bio-cells shapes allowed to associate each bio-cell to a different capacitor model, and to predict the electric-equivalent dimensions characterizing its electric behavior. Finally, the equivalent capacitor model is used to study the influence of bio-cells characteristics variation on human blood cells, with particular attention devoted to liver and lung CTCs-like ones.