A variety of nutrients play essential roles in the formation of red blood cells, including vitamin
B-6, folate and iron. Iron deficiency
anemia, the most common type of anemia, affects as much as 30 percent of the world's population, notes the National Institutes of Health Office of Dietary Supplements."
So if you haven't been tested for those, it would be a good idea to do so. For the iron tests, I suggest ferritin, serum iron, TIBC, and % saturation.