RHD and sickle cell disease: In recent years, demand for blood has generally declined in western countries, probably because of adoption of lower haemoglobin triggers for transfusion and other approaches to avoid transfusion.5, 6 However, there is growing demand for universal blood groups (eg, O Rhesus D [RhD] negative and A RhD negative) and for minor blood groups that might be needed to support multiply transfused populations (eg, patients with sickle cell disease).5