  The erythrocyte sedimentation rate is one of the oldest medical diagnostic
methods whose physical mechanisms remain debatable up to date. Using both light
microscopy and mesoscale cell-level simulations, we show that erythrocytes form
a soft-colloid gel. Furthermore, the high volume fraction of erythrocytes,
their deformability, and weak attraction lead to unusual properties of this
gel. A theoretical model for the gravitational collapse is developed, whose
predictions are in agreement with detailed macroscopic measurements of the
interface velocity.
