When I was diagnosed with UC in 2001, my Hg was between 4 and 5!!!!! YIKES! The doctor told me that he couldn't understand how I was up and walking around!
However, I did not receive a blood transfusion. They did give me iron through an IV. If I remember correctly, I had 3 different appointments for the IV iron. I them saw a Hematologist who put me on a prescription for an iron supplement. This was in addition to meds that were prescribed for my newly diagnosed UC at the time. Eventually, the inflammation from the UC healed and the iron supplements brought my Hg back up to a normal range.
I've had flares since my first UC diagnosis, but none of them ever caused such a drop in my Hg.