Current WHO transfusion guidelines [30] recommend 20 mL/kg of whole blood or 10 mL/kg packed cells for children with Hb ≤6 g/dL, yet standard calculations indicate that this under-treats children with profound anaemia (Hb <4 g/dL) by ~30% [31] Other researchers have shown a modest rise in Hb of 2.5 to 3.3 g/dL following initial transfusion of 20 mL/kg [10,29,32], with post-transfusion Hb remaining <5 g/dL in ~25% of severely anaemic children [10], as we found here. Here, GSTM1 is linked to anemia (phenotype).