1. Important complications of transfusion and their approximate frequency in the UK extrapolated from data from the Serious Hazards of Transfusion (SHOT) scheme 2014 (Bolton‐Maggs 2014) compared with low income countries (WHO 2015).

Transfusion Risk	Frequency in the UK (units transfused) ( Bolton‐Maggs 2014)	Frequency in low income countries ( WHO 2015 )
ABO incompatible red cell transfusion	3.7 in 1 million (10 cases per 2663488 transfusions)	unknown
Transfusion‐related acute lung injury	0.4 in 1 million (10 cases per 2663488 transfusions)	unknown
Transfusion associated circulatory overload	34.1 in 1 million (91 cases per 2663488 transfusions)	unknown