Evaluation of reticuloendothelial function in autoimmune hemolytic anemia using an in vitro assay of monocyte-macrophage interaction with erythrocytes.

We have used an in vitro assay of monocyte-RBC interaction to study the correlation of in vitro monocyte activity with in vivo lysis in patients with autoimmune hemolytic anemia (AIHA). All of 16 patients with a positive direct antiglobulin test (DAT) (0.5 + to 4+) and clinical evidence of hemolysis showed elevated association (ARBC) and phagocytic (PRBC) indices. Of 6 patients studied with a positive DAT (0.5+ to 4+) without clinical evidence of hemolysis, none showed elevated PRBC while 2 showed slightly elevated ARBC. Thus, when using a PRBC index, our assay distinguished between hemolysing and non-hemolysing patients independent of the degree of red cell sensitization as determined by the DAT. In addition, we have studied 6 patients with a positive DAT following alpha-methyldopa therapy. Two of these patients were hemolysing, 4 were not. Again, our assay correlated with in vivo lysis. Finally, we have studied red cells from 11 patients with DAT-negative acquired hemolytic anemia. Seven of these patients showed elevated ARBC and PRBC indices, indicating a possible immune etiology involving extravascular lysis in some DAT-negative acquired hemolytic anemias.