How do i know if i'm experiencing b12 deficieny or iron deficiency anemia?

Blood test: The anemia of iron deficiency give very small red blood cells. The anemia of B12 deficiency causes large rbcs. But even better than looking at the blood count would be to measure the iron andb12 levels. This can be done by you primary physician.

Assuming anemia...: Fe deficiency and B12 deficiency can be distinguished by the size of your red cells. Fe deficiency results in a microcytic hypo chromic anemia, reticulocytopenia and a wide red cell distribution width. B12 and folate (folic acid) deficiency (and pernicious anemia--intrinsic factor deficiency) give rise to a megaloblastic anemia. Red cell indices from a cbc. There are many causes of anemia besides these though.