Serum iron Ferritin The ferritin indicator detects iron deficiency in the blood serum. These tests are needed to diagnose iron deficiency anemia. Iron is essential for the formation of red blood cells. It is the most important component of hemoglobin, a protein that fills red blood cells, which allows them to carry oxygen from the lungs to organs and tissues. Iron is also found in the muscle protein myoglobin and some enzymes.