Peripheral blood from a patient with IgG kappa myeloma is submitted for crossmatching. Red cells form stacks resembling coins on the smear, and aggregation disappears when the sample is diluted with saline. This phenomenon occurs because:
- A High concentrations of monoclonal paraprotein reduce the zeta potential between red cells ✓
- B IgM pentamers bridge adjacent red cells through their antigen-binding sites
- C Cold-reactive anti-I antibodies bind below 30 degrees Celsius
- D Deficiency of spectrin increases membrane deformability and stacking
Correct answer: A. High concentrations of monoclonal paraprotein reduce the zeta potential between red cells
Explanation
Rouleaux formation results from elevated plasma protein, typically monoclonal paraprotein in myeloma or Waldenstrom macroglobulinemia, which diminishes the repulsive zeta potential between red cells and permits stacking. Unlike true cold agglutination caused by IgM antibodies, rouleaux disperses completely with saline dilution, a point tested in serology. Spectrin defects cause hereditary spherocytosis or elliptocytosis, not rouleaux.
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.