Rouleaux

Rouleaux (singular is rouleau) are stacks of red blood cells formed because of the unique discoid shape of these cells in vertebrate body. The flat surface of the discoid RBCs give them a large surface area to make contact and stick to each other forming rouleux. They occur when the plasma protein concentration is high, and because of them the ESR (erythrocyte sedimentation rate) is also increased. Conditions which do this include infections, inflammatory and connective tissue disorders, and cancers. It also occurs in diabetics and is one of the causative factors for microvascular occlusion in diabetic retinopathy.

1. Rouleaux refers to the stacking of RBC

2. The presence of acute phase proteins particularly fibrinogen interacts with sialic acid on the surface of RBC and allows the formation of rouleaux

3. Anaemia by altering the ratio of RBC to plasma increases rouleaux formation and accelerates sedimentation

4. Rouleaux formation is retarded by albumin proteins

Kinetics of Linear Rouleaux Formation
According to Smoluchowski, the kinetics of aggregation of colloids is based on the assumption that each particle is surrounded by a "sphere influence”. Single spherical particles, which undergo Brownian motion collide and sticking of particles. As aggregation proceeds, the average diffusion constant of the aggregate population decreases. The aggregation of red blood cells prgresses in the same manner except that cells are biconcave rather than spherical.