Iron infusions

Hubby will have to have a 2nd infusion of iron tomorrow. He had an infusion
2 weeks ago, when his count had dropped to 9.1 Since then it has dropped
to 8.
He is currently only taking Erbitux every two weeks for stage 4 colon/liver.
Anyone have any experience with what the causes could be for this drop?
Haven't gotten any real answers from the people at the lab, and appointment
with the onc isn't until next week. Didn't know if this count is considered
really low and if it was something to worry about. Thank you, Brenda