COVID-19 and the Coombs test.

In this issue of , Berzuini et al describe immunoglobulin G (IgG) bound to the red blood cells (RBCs) of patients with COVID-19 and associate this bound IgG with increased RBC transfusion requirements. The intrigue behind these observations is not just the high (46%) direct antiglobulin test (DAT) positivity rate, but also the novel finding that eluates (ie, antibodies stripped from the surface of the reactive RBCs) from these DAT-positive patients react not with standard-reagent RBCs but exclusively with RBCs from DAT-negative COVID-19 patients.