ESR (erythrocyte sedimentation rate) is the rate at which red cells settle (sediment) when whole blood is allowed to stand, expressed in mm/hr.
Normal ESR (Westergren method): males 3 to 5 mm/hr, females 5 to 12 mm/hr.
Rouleaux Formation and Sedimentation
Rouleaux is piling of red cells one on the other; piled red cells are heavier, so their presence facilitates sedimentation of whole blood.
Red cells normally remain separate because their negatively charged surface causes mutual repulsion; neutralizing this charge (by fibrinogen or other plasma factors) removes the repelling force and allows rouleaux to form.