COVID-19 and the Coombs test

Abstract

In this issue of Blood, 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.

Elution studies are performed to separate bound Ig from a patient’s RBCs in the setting of an IgG-positive DAT; this separation is typically accomplished using pH or temperature changes. As depicted, the eluates from COVID-19 patients with an IgG-positive DAT did not show agglutination after incubation with commercially available reagent RBCs. However, the same eluates incubated with RBCs derived from other COVID-19 patients showed agglutination. Professional illustration by Patrick Lane, ScEYEnce Studios. AHG, anti-human globulin.