A linearity control system includes a series of linearity control compositions, each thereof includes white blood cell analogs and stabilized red blood cells in a suspension medium. The concentration of the white blood cell analogs in the series of control compositions increases from 0.2×103 to 800×103 analogs per microliter, and the concentration of the white blood cell analogs in at least one control composition is greater than 120×103 analogs per microliter. The stabilized red blood cells facilitate mono-dispersion of the white blood cell analogs in the suspension medium by gently mixing. The control compositions further include platelet analogs, or additionally include reticulocyte and/or nucleated red blood cell analogs. The linearity control system allows the verification of the reportable measurement range and linearity of the measurements of hematology analyzers for white blood cells, red blood cells and platelets in extended concentration ranges.