One of the main sources of efficiency losses in miniaturized turbomachinery is caused by their large relative tip clearances. These small turbomachines are gaining in importance in a number of novel energy systems working with different fluids at closed-loop conditions. The aim of this study is to analyze the effect of pressurization on these tip clearance losses. Both analytical and numerical methods are proposed for their characterization on a reference high-speed miniature radial compressor. Results show the effect of pressurization using four selected working fluids (air, carbon dioxide, propane and isobutane) with inlet pressures in the range of 1-4 bar. While only slight differences in clearance mass flow ratio are found between analytical and numerical approaches, the expected reduction in efficiency provided by the analytical method is not aligned to the numerical results. However, both methods agree in the fact that inlet pressure has low influence on the internal efficiency for all the working fluids simulated.