Copper deficiency is a rare cause of anemia, but also probably underrecognized. It's most common in patients with severe malabsorption syndromes, prolonged TPN (i.e. IV nutrition, if it doesn't include copper), and excess intake of zinc supplements. Anemia from copper deficiency is typically normocytic or macrocytic, and classically (though not always) associated with "ring sideroblasts" on a bone marrow aspirate. In a patient who was persistently anemic despite normal iron, B12, folate, and TSH; who did not have a chronic disease that would suggest anemia of chronic disease (or anemia of renal failure); and who did not have microcytosis that might suggest thalassemia; checking copper is a reasonable thing to do. Or if a bone marrow aspirate had ring sideroblasts without an alternative explanation. In the US, copper deficiency is usually checked with serum copper and ceruloplasmin levels. I have not personally ordered an RBC copper level; although it makes theoretical sense to check it, I would be concerned that the normal range is not well defined, which would increase the likelihood of either a false positives or false negative. Deficiencies of other trace nutrients (except iron of course!) are generally not associated with anemia. I'm sorry that I can't give more specific, individualized medical advice on here.