Red Blood Cells getting bigger?

I have been seeing a dr for about a year she has told be my red blood cells are big which she says is possible leukmia.I thought that it was your white blood cells.She has mention another long word i dont know what that is.I have one more blood test then see a blood dr. for possibl bone marrow scan.She says dont worry most of the time they cant do anything.Could someone please shed a little knowlege on this I would greatly apperiate it,Thank you Debbie