RBC rouleaux formation is best described as what?

• A. Clumps of platelets
• B. White Blood Cell aggregation
• C. Red Blood Cell Stacking
• D. Red Blood Cell fragmentation

Answer: (C)

RBC rouleaux formation is the stacking of red blood cells in long, coin-like columns rather than random clumps. This happens when plasma proteins such as fibrinogen or immunoglobulins increase, reducing the electrostatic repulsion between red cells and allowing them to align in stacks. On a blood smear, you’ll see neat, parallel rows of cells instead of irregular aggregates. This stacking is linked to a higher erythrocyte sedimentation rate because the stacks settle more quickly. It’s different from true clumping of platelets or white blood cells, which appear as irregular, non-ordered aggregates, and from fragmentation, which shows smaller fragments of cells rather than organized stacks.