Spurious Macrocytosis of Antibody-Coated Red Cells

Abstract

Brittin, Geoffrey M., Brecher, George, Johnson, Carole A., and Stuart, John: Spurious macrocytosis of antibody-coated red cells. Techn. Bull. Regist. Med. Techn., 39: 149–153, 1969. We have found that the mean cell volume (MCV) of red cells in autoimmune hemolytic anemia or after sensitization in vitro may form “microagglutinates” of doublets and triplets, even in a 1:50,000 dilution. In such circumstances, electronic counters which register agglutinates as single particles give erroneously low red cell counts (RBC), and the MCV computed as a ratio of hematocrit to this RBC is falsely elevated. Our findings indicate that even vigorous manual mixing of a 1:50,000 dilution of sensitized red cells is not sufficient to produce the correct RBC with the Coulter Counter Model A. In contrast, sensitization of red cells does not produce a change in their MCV when determined with the Coulter Counter Model S, presumably because its efficient automatic mixing system breaks apart the “microagglutinates.” True macrocytosis is known to be associated with hemolytic anemia; but the finding of a very high MCV, when determined by electronic counters other than the Coulter Counter Model S, is suggestive of red cell agglutination, and a Coombs test is indicated.