hi,
By my expirience, my HB would increase about 1 1/2 gram per bag. So if my HB was 6 and i tranfused 2 bags of blood, my Hb would increase to around 9.
Maybe it works differently with everybody else but for me, i find that this method goes well with my body and i've been using it for such a long time as an unofficial guide. I can briefly calculate how many bags of blood i should request from the blood bank.