This is what I heard.
You want to donate blood to this person.
But your blood needs screening, in the event you do not know if
your blood have any problems. Some ppl got Hep B, HIV also
dunno.
You give your blood, and samples is sent to test if your blood is
ok.
At the same time after you donate, the same blood type in the blood
bank, which is declare good and clean, is released to the person
waiting for your blood.
Not only it replaces the correct balance, only clean blood which
pased screening is given to the receipient. Get it?
