We performed extensive simulations of light scattering by granulated coated sphere model using the discrete dipole approximation and varying model parameters in the ranges of sizes and refractive indices of granulated blood cells. We compared these results with predictions of Maxwell-Garnett effective medium theory and independent scattering approximation. Extinction efficiency and Mueller matrix element S11, averaged over azimuthal angles, are accurately described by one of the approximations, except for the intermediate range of polar angles. We discuss dependence of S11 on granule diameter for any fixed angle, showing a distinct maximum, with respect to the solution of the inverse light scattering problem.