ART4 and COVID-19: The biochemical underpinning of rouleaux formation in the blood of COVID-19 patients is the binding of the SP glycoprotein of SARS-CoV-2 (as with the SP of most coronavirus strains) to host cell glycans, in particular, to those with terminal sialic acid (SA) moieties, which are densely distributed on RBCs and other blood cells [43].