Sorry....thought you meant iron when asking about the FE.
I don't think you can actually depend on FE to be an accurate indicator. Once it's elevated over 1000, pretty much anything can cause it to rise. John's would bounce around all the time. We'd see jumps of 1500 points and then drop the next week. So many things can effect it. It seems it would stabilize for months within a specific range and then all of a sudden drop only to hold at that level for a while. The closer we got to 1500 the less erratic it behaved.
Once it gets below 1000, it seems to behave better. But our doc said that even then, you need to look at the entire iron profile.
John had to stop it eventually because his kidneys were being effected. He never got to full dose so it was very slow going for him.
Marlene, wife to John DX w/SAA April 2002, Stable partial remission; Treated with High Dose Cytoxan, Johns Hopkins, June 2002. Final phlebotomy 11/2016. As of January 2017, FE is 233, HGB 11.7, WBC 5.1/ANC 4.0, Plts 146K.