I had a doctor's appointment last Monday and I had a question on my blood test's taken last month. Little did I realize that I was digging up more than I could chew. My RDW on my last blood test was 19 and the high normal end was 15 and I asked my doctor what that meant and he told me that it meant that that the width of my red blood cells were off. (Correct me if I am wrong) So he wanted to check my iron level and my iron level was 13 and low normal was 35-170. I am taking ferrus sulfate 4 times a day. My doctor wants to check for blood in my stool and I might need another colonoscopy. I just don't know if I can put myself through that prep again. Does anyone know what causes iron deficiency anemia?