A treatment system for treating haemorrhagic fluid previously taken from a patient for the purpose of autotransfusion, comprising a treatment unit for treating haemorrhagic fluid, said treatment unit comprising: - a filtration device comprising a filtration membrane for tangential filtration arranged in a housing so as to separate an intake chamber from a discharge chamber, the intake chamber and the discharge chamber each having an inlet (111a; 112a) and an outlet (111b; 112b) for fluids; - a treatment pouch having an inlet and an outlet fluidically connected by a recirculation line to the outlet and to the inlet of the intake chamber of the filtration device, respectively, allowing haemorrhagic fluid to circulate in the recirculation line in a direction going from the outlet of the treatment pouch to the inlet of the treatment pouch through the intake chamber of the filtration device; - an intake line fluidically connected to the recirculation line between the outlet of the treatment pouch and the inlet of the intake chamber of the filtration device making it possible to supply the treatment unit with haemorrhagic fluid taken for the purpose of filtration through the filtration membrane of the filtration device in order to remove from the haemorrhagic fluid a filtrate comprising compounds undesired for autotransfusion; - a transfusion line fluidically connected to the recirculation line between the outlet of the treatment pouch and the inlet of the intake chamber of the filtration device making it possible to recover treated haemorrhagic fluid contained in said treatment pouch; - a discharge line fluidically connected to the outlet of the discharge chamber of the filtration device so as to discharge the filtrate having passed through the filtration membrane from the intake chamber; characterised in that the treatment unit further comprises - a first flow regulation member arranged to regulate the flow in the recirculation line at the outlet of the treatment pouch, and - a dilution line intended to convey dilution fluid into the treatment unit, the dilution line being fluidically connected to the recirculation line at a position between the outlet of the treatment pouch and the inlet of the intake chamber of the filtration device. - a filtration device comprising a filtration membrane for tangential filtration arranged in a housing so as to separate an intake chamber from a discharge chamber, the intake chamber and the discharge chamber each having an inlet (111a; 112a) and an outlet (111b; 112b) for fluids; - a treatment pouch having an inlet and an outlet fluidically connected by a recirculation line to the outlet and to the inlet of the intake chamber of the filtration device, respectively, allowing haemorrhagic fluid to circulate in the recirculation line in a direction going from the outlet of the treatment pouch to the inlet of the treatment pouch through the intake chamber of the filtration device; - an intake line fluidically connected to the recirculation line between the outlet of the treatment pouch and the inlet of the intake chamber of the filtration device making it possible to supply the treatment unit with haemorrhagic fluid taken for the purpose of filtration through the filtration membrane of the filtration device in order to remove from the haemorrhagic fluid a filtrate comprising compounds undesired for autotransfusion; - a transfusion line fluidically connected to the recirculation line between the outlet of the treatment pouch and the inlet of the intake chamber of the filtration device making it possible to recover treated haemorrhagic fluid contained in said treatment pouch; - a discharge line fluidically connected to the outlet of the discharge chamber of the filtration device so as to discharge the filtrate having passed through the filtration membrane from the intake chamber; - a first flow regulation member arranged to regulate the flow in the recirculation line at the outlet of the treatment pouch, and - a dilution line intended to convey dilution fluid into the treatment unit, the dilution line being fluidically connected to the recirculation line at a position between the outlet of the treatment pouch and the inlet of the intake chamber of the filtration device.