Abstract: A device for assessing changes in erythrocyte deformability, such as erythrocyte sickling tendency in a controlled hypoxic atmosphere, comprising: an at least partially transparent inner wall, an at least partially transparent outer wall extending parallel with the inner wall, wherein a gap is present between the inner and outer walls for receiving a blood sample, wherein one of said walls is movable parallel to and relative to the other one of said walls so as to exert a shear force to the sample in the gap, a light source arranged to emit light in a perpendicular direction through overlapping transparent parts of the inner and outer walls, a camera arranged to observe the light from the light source after it is emitted through said transparent parts of the inner and outer walls in order to detect and assess a diffraction pattern therein when a blood sample is present in said gap and the movable wall is being moved, and an oxygen sensor arranged to be in contact with the blood sample in the gap between the i