Rimon et al1 studied the transferrin receptor–ferritin index (TR-F index) in the evaluation of iron deficiency anemia (IDA) in the elderly. The authors concluded that "routine blood tests [have] a very low sensitivity" and that "the TR-F index is much more sensitive." Furthermore, they suggested that a positive TR-F index can eliminate the need for bone marrow evaluation.
Dosh SA. Serum Ferritin vs Transferrin Receptor–Ferritin Index. Arch Intern Med. 2002;162(15):1782-1783. doi: