I have always found the following wording to be a little contradictory? ...
https://www.nhs.uk/conditions/blood-transfusion/"
Risks
Blood transfusions are common and very safe procedures.
All donor blood is checked before it's used to make sure it does not contain serious infections such as hepatitis or HIV.
There's a very small risk of complications, such as:
an allergic reaction to the donor blood
a problem with your heart, lungs or immune system (the body's defence against illness and infection)
The risks will be explained before having a transfusion, unless this is not possible – for example, if you need an emergency transfusion.
Speak to your doctor or nurse if you have any concerns."
