For example , macrocytic hypochromic , due to hookworm infestation leading to not enough of both iron and vitamin B12 or folic acid or following a blood transfusion . When two causes of anemia act simultaneously , e.g. , macrocytic hypochromic , due to hookworm infestation leading to deficiency of both iron and vitamin B12 or folic acid or following a blood transfusion more than one abnormality of red cell indices may be seen .