Low rbc, low hgb, high mcv, normal iron & b12 levels. what is the cause of anemia?

Multiple possible.: If a patient has had recent surgery, that might be the cause. B12 and Folic Acid deficiencies can cause a high MCV (ie, it can represent a nutritional cause). Other possibilites include hemolysis (breaking of red blood cells), kidney disease and other chronic diseases.

Macrocytic anemia: The most common causes of macrocytic anemia are B12 (ruled out for you) and folate (folic acid) deficiencies. Folate (folic acid) deficiency can be caused by diet (very rare - folate (folic acid) is everywhere), celiac disease, alcoholism, or hemolysis (autoimmune process, for example). Rarer causes include aplastic anemia and myelodysplastic syndrome (mds). If not clear to your doc, may need to see hematologist.