Optical flow cytometer for blood cell characterization, comprising: - a flowcell providing a blood cells flow, - at least one light-emitting diode for illuminating blood cells that are flowing in the flowcell, - an epifluorescence module in which a same first lens group is used for focusing the excitation light (8, 4) in the blood cells flow and for collecting fluorescence light coming from each blood cell, and a unitary photodetector for detecting the epifluorescence light coming from the first lens group, - at least one of the following measurement modules: - a light scattering measurement module (5, 19, 24, 25, 26) comprising a second lens group for collecting light emerging from the flowcell, and at least one scattering detection channel (24, 25, 26) comprising a unitary photodetector for detecting scattered light coming from the second lens group and a diaphragm for selecting light along at least one direction, the second lens group being designed to collect the forward scattered light which is scattered by the blood cells flow at angle of 5 degrees with respect to the illumination beam divergence, the scattered light being related to the volume of the blood cells, - an axial light losses measurement module (5, 19, 20, 23, 22) comprising a second lens group for collecting light emerging from the flowcell, and at least one axial light detection channel (20, 23, 22) comprising a unitary photodetector for detecting scattered light coming from the second lens group; and in that it comprises the same second lens group when the optical flow cytometer also includes the light scattering measurement module. - a flowcell providing a blood cells flow, - at least one light-emitting diode for illuminating blood cells that are flowing in the flowcell, - an epifluorescence module in which a same first lens group is used for focusing the excitation light (8, 4) in the blood cells flow and for collecting fluorescence light coming from each blood cell, and a unitary photodetector for detecting the epifluorescence light coming from the first lens group, - at least one of the following measurement modules: - a light scattering measurement module (5, 19, 24, 25, 26) comprising a second lens group for collecting light emerging from the flowcell, and at least one scattering detection channel (24, 25, 26) comprising a unitary photodetector for detecting scattered light coming from the second lens group and a diaphragm for selecting light along at least one direction, the second lens group being designed to collect the forward scattered light which is scattered by the blood cells flow at angle of 5 degrees with respect to the illumination beam divergence, the scattered light being related to the volume of the blood cells, - an axial light losses measurement module (5, 19, 20, 23, 22) comprising a second lens group for collecting light emerging from the flowcell, and at least one axial light detection channel (20, 23, 22) comprising a unitary photodetector for detecting scattered light coming from the second lens group; and in that it comprises the same second lens group when the optical flow cytometer also includes the light scattering measurement module. - a light scattering measurement module (5, 19, 24, 25, 26) comprising a second lens group for collecting light emerging from the flowcell, and at least one scattering detection channel (24, 25, 26) comprising a unitary photodetector for detecting scattered light coming from the second lens group and a diaphragm for selecting light along at least one direction, the second lens group being designed to collect the forward scattered light which is scattered by the blood cells flow at angle of 5 degrees with respect to the illumination beam divergence, the scattered light being related to the volume of the blood cells, - an axial light losses measurement module (5, 19, 20, 23, 22) comprising a second lens group for collecting light emerging from the flowcell, and at least one axial light detection channel (20, 23, 22) comprising a unitary photodetector for detecting scattered light coming from the second lens group; and in that it comprises the same second lens group when the optical flow cytometer also includes the light scattering measurement module.