A hemoglobin of 4.5 can be life threatening. My hematologist told me that if it goes untreated it can lead to cardiac failure. My doctors were concerned and my hemoglobin was initially at 6.9. Since mid-September I've been going to the hospital every week for IV iron infusions.I am perimenopausal and sometimes get heavy periods. I also have another medical issue for which I take Prednisone and steroids over time can deplete red blood cells. Let me tell you I felt like I was hit by a truck when it was at 6.9,I cannot imagine how you feel with a hgb of 4.5!! My hematologist wouldn't even let me leave the hospital the first day I saw him until I got a bag of iron first! Good Luck and feel better soon!