A blood analyser system comprising: a cartridge configured for use in a blood analyser, the cartridge comprising: a blood sample inlet ; a reservoir containing a viscoelastic fluid or a plurality of reservoirs containing separated constitutes of a viscoelastic fluid for subsequent mixing, wherein the viscoelastic fluid comprises a solvent and polymers having a molecular weight between about 50 kDa and 1000 kDa; a mixing chamber connected to the blood sample inlet and the reservoir or the plurality of reservoirs for enabling a blood sample comprising blood cells to mix with the viscoelastic fluid; a shallow and covered microchannel , having an entrance end connected to the mixing chamber and having a width larger than height by a factor of five or more, said micro channel configured for flow the mixed blood sample and viscoelastic fluid such that the blood cells suspended in the viscoelastic fluid align into a two dimensional array in the microchannel as they flow downstream; an optical magnifying objective configured to generate an image of the blood cells aligned in the microchannel; a camera configured to capture the image of the blood cells aligned in the microchannel generated by the objective; a computer configured to process the captured image to obtain a blood cell concentration, wherein the blood cell concentration is calculated by Con = N × D FOV × H , where Con is a concentration of red blood cells, N is a number of red blood cells, FOV is an optical field of view area, and H is the height of the microchannel. a cartridge configured for use in a blood analyser, the cartridge comprising: a blood sample inlet ; a reservoir containing a viscoelastic fluid or a plurality of reservoirs containing separated constitutes of a viscoelastic fluid for subsequent mixing, wherein the viscoelastic fluid comprises a solvent and polymers having a molecular weight between about 50 kDa and 1000 kDa; a mixing chamber connected to the blood sample inlet and the reservoir or the plurality of reservoirs for enabling a blood sample comprising blood cells to mix with the viscoelastic fluid; a shallow and covered microchannel , having an entrance end connected to the mixing chamber and having a width larger than height by a factor of five or more, said micro channel configured for flow the mixed blood sample and viscoelastic fluid such that the blood cells suspended in the viscoelastic fluid align into a two dimensional array in the microchannel as they flow downstream; a blood sample inlet ; a reservoir containing a viscoelastic fluid or a plurality of reservoirs containing separated constitutes of a viscoelastic fluid for subsequent mixing, wherein the viscoelastic fluid comprises a solvent and polymers having a molecular weight between about 50 kDa and 1000 kDa; a mixing chamber connected to the blood sample inlet and the reservoir or the plurality of reservoirs for enabling a blood sample comprising blood cells to mix with the viscoelastic fluid; a shallow and covered microchannel , having an entrance end connected to the mixing chamber and having a width larger than height by a factor of five or more, said micro channel configured for flow the mixed blood sample and viscoelastic fluid such that the blood cells suspended in the viscoelastic fluid align into a two dimensional array in the microchannel as they flow downstream; an optical magnifying objective configured to generate an image of the blood cells aligned in the microchannel; a camera configured to capture the image of the blood cells aligned in the microchannel generated by the objective; a computer configured to process the captured image to obtain a blood cell concentration, wherein the blood cell concentration is calculated by Con = N × D FOV × H , where Con is a concentration of red blood cells, N is a number of red blood cells, FOV is an optical field of view area, and H is the height of the microchannel. <EOS>