A flow cell includes a housing, a window member, and a pressing member. The housing includes a cell channel in which a sample flows through, has, on at least one end side of the cell channel, an opening communicating with the cell channel, and has a flat surface at an edge of the opening. The window member has a lens portion at a central portion and a peripheral edge portion whose one surface and the other surface are flat. In the window member, one surface of the peripheral edge portion is provided facing the flat surface of the housing so as to seal the opening.

The invention relates to a method of determining a concentration of a substance in a cell suspension, said method comprising the following steps: determining the concentration of the substance by: using the results of absorption measurements performed at n local sample volumes contained at different average chamber heights of a chamber arrangement comprising the cell suspension and local substance concentration in said respective local sample volumes determined based on said respective absorption measurements; using a substance concentration model comprising local substance concentration as a function of chamber height, anddetermining the substance concentration as the infinite chamber height substance concentration using said substance concentration model and the determined local substance concentrations, wherein n is at least 2, such as at least 3, such as at least 4, wherein, optionally, the cell suspension is whole blood and the substance is Hb and wherein the method further comprises determining cRBC based on the determined Hb concentration and a determined Mean Corpuscular Hemoglobin (MCH). The invention also relates to a system for executing the method.

A detecting device for a medium inside a tube portion comprises at least one light source being arranged at a first position relative to the tube portion adapted to be transilluminated with light and being configured to irradiate light onto the tube portion, a detector unit being arranged at a second position relative to the tube portion and being configured to receive light from the at least one light source passed through the tube portion and to analyze a medium inside the tube portion in a spatially resolving manner, and a homogenizing device being arranged at a position between the at least one light source and the tube portion and being configured, for detecting and quantifying differences in brightness due to local differences of the medium inside the tube portion, to create a homogenous and/or isotropic distribution of the light from the at least one light source before the light enters into the tube portion.

A detecting device for a medium inside a tube portion comprises at least one light source being arranged at a first position relative to the tube portion adapted to be transilluminated with light and being configured to irradiate light onto the tube portion, a detector unit being arranged at a second position relative to the tube portion and being configured to receive light from the at least one light source passed through the tube portion and to analyze a medium inside the tube portion in a spatially resolving manner, and a homogenizing device being arranged at a position between the at least one light source and the tube portion and being configured, for detecting and quantifying differences in brightness due to local differences of the medium inside the tube portion, to create a homogenous and/or isotropic distribution of the light from the at least one light source before the light enters into the tube portion.