A peripheral smear from a 65-year-old man with back pain and normocytic anemia shows red cells stacked in linear columns resembling a stack of coins. Which statement correctly distinguishes this finding from red cell agglutination?
- A It resolves on warming the sample to 37 degrees Celsius
- B It reflects cross-linking of red cells by IgM antibodies against carbohydrate antigens
- C It disperses when a drop of saline is added to the blood film ✓
- D It is associated with hereditary spherocytosis and a positive osmotic fragility test
Correct answer: C. It disperses when a drop of saline is added to the blood film
Explanation
Rouleaux formation results from elevation of plasma proteins, especially fibrinogen and paraproteins, which reduces the zeta potential between red cells; the stacks disperse with saline dilution because the effect is nonspecific. True agglutination is caused by specific antibodies cross-linking antigen-bearing cells and persists despite saline. Cold agglutinins may resolve on warming, but that property does not describe 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.