Microfluidic cytometers based on coulter principle have recently shown a great potential for point of care biosensors for medical diagnostics. In this study, the design of coulter based microfluidic cytometer is investigated by using electrical circuit simulations. We explore the effects of physical dimensions of the microelectrodes, the measurement volume, size/morphology of the targeted cells, electrical properties of the reagents in the measurement volume, and, the impedance of external readout circuit, on the sensitivity of the sensor. We show that the effect of microelectrode's surface area and the dielectric properties of the suspension medium should be carefully considered when characterizing the output response of the sensor. In particular, the area of microelectrodes can have significant effect on cells electrical opacity( the ratio of the cell impedance at high to low frequency) which is commonly used to distinguish between sub-population of the target cells( e.g. lymphocytes vs monocytes when counting white blood cells).Moreover, we highlight that the opacity response vs frequency can significantly vary depending upon whether the absolute cell impedance or the differential output impedance is used in the calculation. These insights can provide valuable guidelines for the design and characterization of coulter based microfluidic sensors.