Imaging erythrocyte sedimentation in whole blood

The erythrocyte sedimentation rate (ESR) is one of the oldest medical diagnostic tools. However, currently there is some debate on the structure formed by the cells during the sedimentation process. While the conventional view is that erythrocytes sediment as separate aggregates, others have suggested that they form a percolating gel, similar to other colloidal suspensions. A direct probing of the structures formed by erythrocytes in blood at stasis is then required to settle these discrepancies. Here, we report observations performed with three different optical imaging techniques: direct light transmission through thin samples, two-photon microscopy and light-sheet microscopy. All techniques revealed a dynamic structure of a channeling gel but with differences in the resolved details. A quantitative analysis of the erythrocyte related processes and interactions during the sedimentation need a further refinement of the experimental set-ups.