What term describes the presence of two distinct populations of red blood cells in a transfusion patient?

• A. Dimorphic population of transfused red blood cells
• B. Single homogeneous population
• C. Isoagglutination
• D. Polyagglutination

Answer: (A)

Two distinct populations of red blood cells in the same patient occur when donor cells persist alongside the patient’s own cells. This creates a dimorphic population, meaning two different cell populations are circulating with different antigenic backgrounds. In practice, this can show up as mixed-field patterns on testing, such as mixed-field agglutination, reflecting the coexistence of donor and recipient cells after transfusion. Over time, as donor cells are cleared, the population becomes homogeneous again. The other terms describe different phenomena: single homogeneous population is just one cell type, isoagglutination is antibody-driven clumping of isoantigens, and polyagglutination involves broad, non-specific reactivity due to bacterial modification of RBC antigens, none of which describe two competing RBC populations.