Peripheral smear from a patient with multiple myeloma shows red blood cells stacked like coins, and the erythrocyte sedimentation rate is markedly elevated. Which mechanism explains these findings?

• A Paraprotein binds sialic acid residues and increases the deformability of the red cell membrane
• B Excess paraprotein neutralizes the negative surface charge of erythrocytes, reducing zeta potential and permitting aggregation ✓
• C Autoantibodies directed against Rh antigens cause immune-mediated rosetting of red cells
• D Defective spectrin assembly produces rigid spherocytes that align in columns

Explanation

Normal red cells repel each other because negatively charged sialic acid residues create a zeta potential. High concentrations of monoclonal immunoglobulin screen these surface charges, allowing the cells to aggregate into rouleaux, which sediment rapidly and raise the ESR. This differs from agglutination caused by cold antibodies, which persists at low temperature and involves direct antigen-antibody bridging rather than charge screening. Spherocytes reflect membrane loss, not stacking.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.