CountBright™ absolute counting beads are a calibrated suspension of microspheres that are brightly fluorescent across a wide range of excitation and emission wavelengths (UV to 635 nm excitation and 385-800 nm emission). CountBright™ absolute counting beads are mixed with the cell sample and assayed via flow cytometry. By comparing the ratio of bead events to cell events, absolute numbers of cells in the sample can be calculated. Because CountBright™ beads are mixed in the test sample, absolute cell counts using this single-platform method are more accurate and less complicated than cell concentration determined using multiple-platform testing. CountBright™ absolute counting beads can be used with any sample type, including no-wash/lysed whole blood.