Rouleaux formation

Stacking of red blood cells into formations that resemble rolls of coins, usually due to increased plasma proteins (fibrinogen, immunoglobulins). Associated with elevated erythrocyte sedimentation rate, inflammation (connective tissue disease, trauma/surgery), infection, plasma cell disorders (multiple myeloma, Waldenström's macroglobulinemia), malignancy (carcinoma, lymphoma), pregnancy, liver cirrhosis, or artifacts if a blood smear is prepared poorly.