Hello John
GCSF (or Granulocyte colony-stimulating factor) injections are used by patients, including me, to boost white cell production in the blood when their production has been affected by Revlimid, which lowers the neutrophil count. In my case, my normal neutrophil count is around 3.0. When I resumed Revlimid, my count went down to to 0.2.
A level of 0.5 is considered to be neutropaenic and that's when you end up in hospital in isolation etc.
It's worth bearing in mind that there have been a number of previous forum posts on this subject concerning the back throbbing pain that these injections can cause. If you do have to go onto them, I would strongly suggest pain control with your Consultant.
Kevin