Often the amount of blood that is lost is quite small, but excessive bleeding during a spine fusion is always a possibility.
Some medications can increase the amount of blood loss.
These medications should be discontinued 10-14 days before surgery. Spinal surgery cannot be done safely if your blood does not clot. If there is an anticipated large blood loss, the surgeon may order autologous blood donation. This process means that you donate your own blood to be returned to you if needed in the hospital. Donating blood will make you anemic and your doctor should recommend starting an iron supplement if donation is done.